I have had the usual symptomatic water overflow out of the dishwasher air gap on the top of my sink countertop. After replacing the countertop with granite and relocating the air gap hole, I replaced the hose from the air gap to the disposal and insured there was no blockage in the disposal and new hose. Yet I have so much water pressure coming from the dishwasher that it shoots out of the air gap vent. I confirm the water is draining into the disposal from the air gap vent but it seems there is so much water or the pressure is so great the system can't handle the amount of water being discharged and backs up into the air gap. I've even looped the extra amount of hose from the dishwasher to the air gap above the disposal drain height to see if that would solve this. It did seem to take some of the pressure off the water coming out of the air gap but it still spews out. After searching and reading all the posts regarding this usually common issue, I'm at a loss. Anyone have any ideas?

Speedball1, our resident plumber, tells us he never uses air gaps nor do I. They are intended to prevent back siphoning but you can do the same with a high loop in the drain hose. Run the drain out of the washer all the way to just under the counter and strap it to the cabinet, then to your disposal. The problem you are experiencing should not happen but we don't know if you added a new washer or who did your plumbing. Something's is causing a partial blockage, you did not accidentally reverse the two hoses did you? The drain from the machine goes to the smaller of the two tubes of the air gap.

Ok I just conducted a little experiment and now I have no idea what the problem is. I disconnected the large hose at the disposal so that it was still connected to the air gap vent. I put the unattached end into a bucket and started the dishwasher. When the dishwasher drained water and water came out of the larger hose unobstructed into the bucket, water still came out of the air gap vent, same as before!

Is it possible that the dishwasher is draining with too much pressure?

Dish washer pressure can't get stronger than day1. It is the same dishwasher, right? The hose leading to the air gap from the machine should be nearly straight, no loop so cut it shorter. Is the air gap the original or did you replace it when the counters went in? There is a very slim chance that you have a bad air gap. They are so simple the chances are slim. I'd remove it and just strap the drain I described earlier in the post. They are a pain and Speedball1 says they aren't needed although some cities require them to be up to code.

Haven't changed dishwasher. Same as when we moved in, but we were having this issue then too. I've replaced the original air gap with two new ones, the first the same style and the second a different style. Same result each time.

Hopefully someone might have an idea. I'd like to try and keep it up to code by keeping the air gap.

So you've had this issue all along, not tied to the new counters. Do you know that your city building code requires a gap? Dave, code is for construction and you doing a DIY have a bit of latitude, take it out.

Yes local code here requires the air gap. If I was staying in the house I'd solve it with your solution but we're preping to sell soon and it'll have to pass inspection so I'd rather take care of it per code. I also want to know for my own education why it's happening.

So if there's anyone else out there with any ideas, let me know! Thanks in advance.

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Originally Posted by daveskee

Yes local code here requires the air gap. If I was staying in the house I'd solve it with your solution but we're preping to sell soon and it'll have to pass inspection so I'd rather take care of it per code. I also want to know for my own education why it's happening.

So if there's anyone else out there with any ideas, let me know! Thanks in advance.

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Are there any kinks in the 7/8" hose going into the disposal?

Are you using the correct inlets and outlets on the air-gap?

The smaller inlet takes the hose from the dishwasher and the larger outlet gets the hose going into the disposal.

Also, check the inlet on the disposal to be sure the plug has been completely removed.

Growler's correct about checking the disposals knock out plug, seen many still partially attached. However you said it still happens when you put the discharge hoes into a bucket. Since it was a new hose I'm stumped on this problem. Before we yell uncle please double check the two hoses going to the air gap. Growler and I both mentioned the smaller hose goes between the washer and the air gap. Sorry I could not solve this issue Dave.

There are no kinks in the 7/8" hose and the correct outlets on the air gap are hooked up correctly. Small inlet from the dishwasher and larger outlet to the disposal. Knockout plug is not present as I've reached into the disposal and felt the open hole with my finger. I've even put a small screwdriver into the inlet and it came through into the disposal freely. I even felt the water shooting into the disposal from the 7/8" hose inlet as the dishwasher drained. But listen to this, as the water is shooting into the disposal as it should, water is still coming out of the air gap! There seems to be too much pressure. So much so that if I take off the metal cover on the air gap, the water shoots up about 8-10" out of the top of the air gap.

As far as I know, you can't regulate the drainage pressure from the dishwasher.

Could a blockage in the dishwasher or dishwasher drainage line cause increased pressure? I assume it would just do the opposite and cause less water pressure.

Thanks for the tips guys but I think I've thought of everything that's been suggested so far. I can't believe no one else has had this problem. Well I'm holding out hope that this thing won't beat me and am still open to suggestions if there are any others out there!

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Originally Posted by ballengerb1

Speedball1, our resident plumber, tells us he never uses air gaps nor do I. They are intended to prevent back siphoning but you can do the same with a high loop in the drain hose. Run the drain out of the washer all the way to just under the counter and strap it to the cabinet, then to your disposal. The problem you are experiencing should not happen but we don't know if you added a new washer or who did your plumbing. Somethings is causing a partial blockage, you did not accidently reverse the two hoses did you? The drain from the machine goes to the smaller of the two tubes of the air gap.

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In our code book we have to install an air gap, and I do not agree with the notion that you don't need one to prevent back flow into the dishwasher. If a doit-yourselfer has a stopped up sink and his friend tells him to fill up the disposal side of the sink with water and stop up the other side of the sink and then turn on the disposal, Where do you suppose the water is going to go, with all of the contaminates that have collected in the disposal and the hose leading from the dishwasher.

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Originally Posted by daveskee

I have had the usual symptomatic water overflow out of the dishwasher air gap on the top of my sink countertop. After replacing the countertop with granite and relocating the air gap hole, I replaced the hose from the air gap to the disposal and insured there was no blockage in the disposal and new hose. Yet I have so much water pressure coming from the dishwasher that it shoots out of the air gap vent. I confirm the water is draining into the disposal from the air gap vent but it seems there is so much water or the pressure is so great the system can't handle the amount of water being discharged and backs up into the air gap. I've even looped the extra amount of hose from the dishwasher to the air gap above the disposal drain height to see if that would solve this. It did seem to take some of the pressure off of the water coming out of the air gap but it still spews out. After searching and reading all the posts regarding this usually common issue, I'm at a loss. Anyone have any ideas?

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After all of the things that you have tried I think I would go to the hardware store and invest in a new air gap, they come in different designs and it could be that there is a problem with your's and a new one might stop the problem.

One thing I will mention but I am sure that you have checked is to make sure that there is not kink in the 7'8 inch hose from the air gap to the disposal, also make sure that the 7/8 inch hose has a downward slope all the way to the disposal.

I've replaced the old air gap with two different types and same result. No kink and the 7/8" hose is downward sloped. Already addressed these. Any other ideas?

Sorry Dave but I've run out of ideas and it isn't feasible to swap out a dishwasher to try another. Seems like you've done everything else. I'm sure the dishwasher people won't like this idea but you could try reducing the drain tube between the machine and the air gap. Try partially crushing the drain hose with a C clamp to see if it fixes your problem and doesn't create a new one.

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Originally Posted by letmetellu

In our code book we have to install an air gap, and I do not agree with the notion that you don't need one to prevent back flow into the dishwasher. If a doit-yourselfer has a stopped up sink and his friend tells him to fill up the disposal side of the sink with water and stop up the other side of the sink and then turn on the disposal, Where do you suppose the water is going to go, with all of the contaminates that have collected in the disposal and the hose leading from the dishwasher.

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"If a doit-yourselfer has a stopped up sink and his friend tells him to fill up the disposal side of the sink with water and stop up the other side of the sink and then turn on the disposal, Where do you suppose the water is going to go?"
With a air-gap it's going to go all over the counter top and kitchen floor. That's where.
And what idiot would advise anyone to pour more water in a clogged sink and then attempt to use a disposal to clear the clog. I have been putting in dishwashers in condos and new houses since 1979 using a high loop instead if counter top air gap. In all those years, and in the hundreds of installations we have done, we haven't had even one complaint about a high loop misfunctioning.
I KNOW that the air-gaps can't make that statement because we get complaints about counter top floods from time to time here in the plumbing page.
LetmetellU, perhaps you and Growler are forced, by code, to use counter top air-gaps but here we have a classic case of mechanical versus natural. Sort of like "What is more likely to fail?" A regular vent out the roof or a AAV?
A high loop or a counter top air-gap? In my area we have a choice. We went with a high loop. I rest my case. Tom

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Originally Posted by speedball1

"If a doit-yourselfer has a stopped up sink and his friend tells him to fill up the disposal side of the sink with water and stop up the other side of the sink and then turn on the disposal, Where do you suppose the water is going to go?"
With a air-gap it's going to go all over the counter top and kitchen floor.

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Sure -- And without the air gap it's going to go right into the hose and then down the hose and contaminate the dishwasher.

I hate to break it to you, Tom, but your reply was almost verbatim the example I give during class for why an air-gap is required under the UPC.

I'm not going to get into a pissing match with you over which code is superior over the other, but I think it should be noted that it was you who illustrated the point.

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And what idiot would advise anyone to pour more water in a clogged sink and then attempt to use a disposal to clear the clog.

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You're kidding, right?

Think back on all of the truly bad advice you've left negative feedback on, Tom.

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I have been putting in dishwashers in condos and new houses since 1979 using a high loop instead if counter top air gap. In all those years, and in the hundreds of installations we have done, we haven't had even one complaint about a high loop misfunctioning.
I KNOW that the air-gaps can't make that statement because we get complaints about counter top floods from time to time here in the plumbing page.

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Y'know, I've yet to encounter the situation you describe in a properly installed air gap.

Usually if the air gap has failed, it is because the user failed to rinse the dishes off or the limiter on the discharge pump has failed.

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LetmetellU, perhaps you and Growler are forced, by code, to use counter top air-gaps but here we have a classic case of mechanical versus natural. Sort of like "What is more likely to fail?" A regular vent out the roof or a AAV?
A high loop or a counter top air-gap? In my area we have a choice. We went with a high loop. I rest my case. Tom

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Sure -- But your example contaminated the dishwasher and the dishes in the dishwasher (something the user couldn't possibly be aware of), while the other example merely flooded the counter top and kitchen floor (the user would have to be deaf, dumb and blind to not figure out there was a problem if this should happen).

Great rebuttal Growler. Good points all! One problem. Would you care to check back on the complaints we have got on air-gaps versus high loops? Gee! That's correct! We haven't got any high loop complaints have we? You're correct about the disposal pumping gray water back into the dishwasher if some fool were to advise clearing a clogged drain line by filling up the sink with water and turning on the disposal. Let's see how many complainbts we have got over the years on that scenario. Oops! Can''t find any of those either. Even if the drain line were cloggec and standing water in the tub it still wouldn't drain back into the DW unless some total idiot ran the disposal. I can only repeat, "here we have a classic case of mechanical versus natural. Sort of like "What is more likely to fail?" A regular vent out the roof or a AAV?
A high loop or a counter top air-gap?, (This is a no brainer) In my area we have a choice. We went with a high loop. I rest my case."
I was impressed. While your rebuttal was great and you took it point by point the very complaints and posts by askers prove that while your concerns and arguments sound valid they don't hold up when you check back on askers complaints of the same nature. However, I enjoyed your reply. Have a great week end ! Tom

I think that anyone that would call the water in a stopped up disposal, the nastiest household fixture in the entire house, even nastier than the commode, gray water is an idiot.

First of all thanks for calling me a idiot. Now, just what's the discharge from tubs, showers, lavatories, washers and kiutchen sinks called? Gee! Whadda you know! It's called "gray water" as per against "fecal matter". I would be most interested in your name for it. In the meantime if you're going to insult someone and call him a idiot get your definitions correct before you do it or you might end up looking like one yourself.

Perhaps whoever coined the term ''gray water'' for the discharge from sinks, showers, etc. was an idiot, but it is a common term for it. I wouldn't call a highly trained, experienced professional an idiot for using a common term. Those that persist on calling people idiots on AMHD can become former members.

I like the idea of restricting the flow from the dishwasher. It would have been my first suggestion. The C-clamp will be a good first try. Before selling the house, you may want to put something inside the hose or pump outlet out of view. I never have posted much to plumbing because when I came here, Tom was posting better answers than I could.

You do want to fix it. In many cases a problem is still yours after you sell the house.

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Originally Posted by speedball1

Would you care to check back on the complaints we have got on air-gaps versus high loops? Gee! That's correct! We haven't got any high loop complaints have we?

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Well, given the nature of the failure of a high loop should it fail, no one is going to notice.

Do you check your dishwasher to see if there is any contaminated water sitting in the bottom of it? Not that you would know it was contaminated, of course.

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You're correct about the disposal pumping gray water back into the dishwasher if some fool were to advise clearing a clogged drain line by filling up the sink with water and turning on the disposal. Let's see how many complainbts we have got over the years on that scenario. Oops! Can''t find any of those either.

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And what if there was a partial clog in the discharge line?

Some of the waste water would pump past the blockage, but most of it would gravity drain back into the dishwashers sump.

And also, we're talking about connecting the drain hose to the disposal.

Most Plumbers I know rough in a kitchen drain with a partition cross and pipe the discharge hose into a separate trap -- Without the air gap as a tell-tale, how would you even know a problem exists with a high loop?

The discharged water certainly isn't going to back up into the sink if the discharge hose is plugged or partially plugged.

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Originally Posted by labman

I wouldn't call a highly trained, experienced professional an idiot for using a common term.

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No?

Yet you have no problem with disagreeing mightily and vociferously with 'highly trained, experienced professionals' such as myself, Labman.

"Well, given the nature of the failure of a high loop should it fail, no one is going to notice.
Do you check your dishwasher to see if there is any contaminated water sitting in the bottom of it? Not that you would know it was contaminated, of course."

If a higfh loop fails you won't have to check the sump to find out.
Simply open the door and all the water that was used will come gushing out.
However, That's never happened in all the dishwashers my company's installed or has it ever been a complaint here in the [plumbing page.

"And also, we're talking about connecting the drain hose to the disposal."
Most Plumbers I know rough in a kitchen drain with a partition cross and pipe the discharge hose into a separate trap -"

we don't complicate things in my area, We connect to the disposal and if there's no disposal we connect to a branch tailpiece.

-" Without the air gap as a tell-tale, how would you even know a problem exists with a high loop?"

This question has been answered earlier. You'd have a flood the moment you opened the dishwasher door.

Dave, you got to problem with your air -gap? Run a high loop and forget it.
Regards, Tom

I would normally be out of this by now because we've got some great pros in discussion. Dave did you ever try my suggestion about restricting the discharge? Since you seem to want to keep the air gap (don't do it) you could throttle down the volume of your dishwasher power drain.

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Originally Posted by speedball1

First of all thanks for calling me a idiot. Now, just what's the discharge from tubs, showers, lavatories, washers and kiutchen sinks called? Gee! Whadda ya know! It's called "gray water" as per against "fecal matter". I would be most interested in your name for it. In the meantime if you're gonna insult someone and call him a idiot get your definitions correct before you do it or you might end up looking like one yourself.

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I have reread all of the post that I have posted on this subject and I can not find where I called any individual, by name or by suggestion, an Idiot. All I was trying to do was make a point about how nasty the water is that goes through a disposal.

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Originally Posted by iamgrowler

Usually if the air gap has failed, it is because the user failed to rinse the dishes off or the limiter on the discharge pump has failed.

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I'm not sure what the limiter on the discharge pump is but is that something that the original poster should look at?

I haven't tried restricting the drain hose yet but that's my next step. I'll post the results when I'm done. Thanks for all the input.

Last suggestion Dave,

This shouldn't be a question about what's better, a air-gap or a high loop, this should be about what works for you. You've fought your air-gap about as far as you can take it. Choking or restricting the discharge by clamping the hose is a last ditch effort and will set up back pressure in the pump. I don't know if this will be harmful to the unit or not since we have never been faced with your problemin in our area but I do know restricting the discharge of anything can't be beneficial.
If everything else fails with your air-gap then remove it, place a chrome cock hole cover or a soap dispenser in its place and run a high loop on the discharge hose. Run the loop as high as it will go under the cabinet and secure it with a pipe strap,(see image) and put this all behind you. This is not to say the other "pro air-gap" experts are wrong. This is about getting your problem solved in the fastest, easiest way and I believe a high loop may be the answer. Good luck, Tom

Hear, hear Speedball. Codes are important, don't get me wrong, but they are not absolute physical laws. At the time my home was built air gaps were not required but they are now. Its just a new law to avoid worst case scenarios not the day to day issue. Where I live drywall was not code until 1975, does that mean it was unsafe? Some codes are driven by lobby groups and unions and are not necessarily mandated by physical laws. Many DIY repairs are not always code but improvisation is sometimes needed when the original up to code part fails.

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Originally Posted by ballengerb1

Hear, hear Speedball. Codes are important, don't get me wrong, but they are not absolute physical laws.

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I'm reminded of the arguments I've had with architects, designers and homeowners over the years:

'But Plumbing Codes are arbitrary and they certainly don't apply to me'.

My usual pat response is, "They most certainly are not arbitrary and they most definitely do apply to you."

Period.

Quite frankly, I'm appalled by yours and Tom's answers to this problem, Dave.

If he lived in the 90% of the country where high loops are accepted, then I wouldn't have word one to say on the subject -- But to advise someone to defy the prevailing code in their community is just wrong.

Period.

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At the time my home was built air gaps were not required but they are now.

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I don't know if you're still out in the field or not, but the old policy of 'Grandfathering' in older installations that are no longer up to code is a thing of the past -- The general consensus is that if you open it up (expose it to view), you must bring it up to code.

Period.

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Its just a new law to avoid worst case scenarios not the day to day issue.

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It isn't, actually.

If you read the code book Tom is operating from -- A "highloop" is an acceptable alternative (under the IPC and the SPC) to an approved airgap -- Meaning that an airgap is an additional accepted alternative.

Most high end Plumbers in jurisdictions covered by the IPC and the SPC opt for counter mounted airgaps or Johnson Tee's -- In the unwritten rules of Plumbing, 'Cover Thine Own Butt' is in the top 5.

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Many DIY repairs are not always code but improvisation is sometimes needed when the original up to code part fails.

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Wrong.

It isn't the code that has failed -- It is something in either the installation or the appliance that has failed.

Tom has stated that there are a number of posts regarding the failure of counter mounted airgaps -- I'm not going to dispute this, because I can visualize installation snafu's where this might occur, but in over twenty years of owning and running a Plumbing company, I have never once had this happen to any of my installations.

Growler, Growler, Growler,

The problem with you younger, "by the book" plumbers is that the "book" never tought you to improvise or think outside the box. Everythings black and white to you. "If it ain't code, it ain't right". You appear to worry more about code then you do about results. Did you even take the time to read my last post. Let's get Daves dishwasher workingt for him and quit
Hassling about the pros-and cons of air-gaps. He's tried three air-gaps with the same result. I gave him a solution. Do you have anything better??

Pumps have a pressure/volume curve. If you increase the back pressure by using a restriction, the volume delivered will decrease. It is easier to destroy a pump with too low of back pressure than too high. Try the C-clamp. If it works, go to something more permanent. Even a partial kink in the hose might do. Keep it out of sight so nobody fixes it. If I were going to live in the house, I would have a high loop installed long before this. When you sell it, it may be inspected and you may be presented with the bill to fix all the code violations.

I point out mistakes, which upsets some people when a non plumber catches theirs, but don't call people idiots here.

I might just have cleared up the mystery of why his air-gap clogs up.
I went over to the appliance page and picked some brains. It seems that mid and upper level dishwashers have grinders that grind the food up so it won't clog a air-gap. The lower end ones use the pump to grind the food particles. If Dave had a faulty grinder or didn't wash the plates good this could be the reason. This is not a solution, ( I gave that in a earlier post) but just one possible explanation. Regards, tom

I don't understand how a faulty grinder or pump would result in the increase in water pressure draining from the dishwasher. Speedball1, could you explain that to this novice?

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Originally Posted by daveskee

I don't understand how a faulty grinder or pump would result in the increase in water pressure draining from the dishwasher. Speedball1, could you explain that to this novice?

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Sorry Dave, My bad! In the confusion over which was the best, air-gap or high loop, I lost track of your original complaint and was thinking the air-gap overflowed due to blockage in the dischage. I apologize for my error. However, there have been only two solutions offered. One was to choke down on the volume entering the air-gap and I'll repeat mine. If everything else fails with your air-gap then remove it, place a chrome cock hole cover or a soap dispenser in its place and run a high loop on the discharge hose. Run the loop as high as it will go under the cabinet and secure it with a pipe strap,(see image) and put this all behind you. This is not to say the other "pro air-gap" experts are wrong. This is about getting your problem solved in the fastest, easiest way and I believe a high loop may be the answer.
If restricting the flow to the air-gap doesn't help I would give some serious thought to my solution. Anyway you go I wish you the best of luck. Tom.

I found this web site while trying to find help with the very same problem described by daveskee. Did he ever get his trouble resolved?

It looks to me like the air gap that came with my dishwasher is just a poor design that doesn't have a chance of properly draining the water at the kind of pressure and volume as delivered by the dishwasher pump. I tried looking at replacements on-line but all of the photos show them with decorative covers in place so I can't see if the gap itself looks any better than the one I have. Also, daveskee mentioned going through several replacements without success, so I'm thinking that these air gaps are all pretty similar and replacing mine probably wouldn't solve anything. But does anyone have a suggestion for a particular model, should I decide to go that way?

I've found the air gap/high loop controversy interesting. I don't know what the Baltimore City code says about them.

Thank you.

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Originally Posted by daveskee

I have had the usual symptomatic water overflow out of the dishwasher air gap on the top of my sink countertop. After replacing the countertop with granite and relocating the air gap hole, I replaced the hose from the air gap to the disposal and insured there was no blockage in the disposal and new hose. Yet I have so much water pressure coming from the dishwasher that it shoots out of the air gap vent. I confirm the water is draining into the disposal from the air gap vent but it seems there is so much water or the pressure is so great the system can't handle the amount of water being discharged and backs up into the air gap. I've even looped the extra amount of hose from the dishwasher to the air gap above the disposal drain height to see if that would solve this. It did seem to take some of the pressure off of the water coming out of the air gap but it still spews out. After searching and reading all the posts regarding this usually common issue, I'm at a loss. Anyone have any ideas?

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Just a guess but some times small chicken bones or tooth picks can get stuck in the dishwasher discharge hose. They are to long to turn the corner in the air gap but can fall back down the hose and out of sight, then come right back up and plug a new air gap.

If you pop the top off the air gap and remove the top plug. With the dishwasher set on discharge … close the door on the dish washer for about one second... what ever is in the hose will come out the top of the air gap. Put it back together and test it.

Just an old handyman but I have seen it three or four times over the years.

Happy trails
Mark

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I'm thinking that these air gaps are all pretty similar and replacing mine probably wouldn't solve anything. But does anyone have a suggestion for a particular model, should I decide to go that way?

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ElGlom-0, I have a solution for you that has worked without complaints or call backs in my area for years. Remove the old air gap and install a chrome cock hole cover in its place. Now run a high loop air gap by replacing the discharge hose and looping it up as high as it will go in the cabinet and securing it with a pipe strap 0or band iron. You may now connect to the disposal and forgrt about any more counter top back ups. Good luck, Tom

I have read the lengthy and heated answers and comments to this question.

I have just returned from a client who has a Jen-Air DishWasher that "smells like dirty water".
I am having the same problem as Daveskee and El Glam-O.

The installation of an air-gap allows water to erupt from the air-gap during the pump/drain cycle of the DW. And, sorry Speedball1, but draining a sink-full of water from the single-basin sink with disposal (prior to air-gap installation) allows water to return up the DW drain line and back into the disposal. This may well be due to a plumbing vent problem "downstream" from the disposal, but regardless, it seems physically impossible for this to happen.

I agree with Daveskee that the problem does indeed seem to be that the DW pumps water too fast.. . at least faster than the hose downstream from the air gap can allow to pass.

Please, any suggestions or further insight into how to remedy the situation would be greatly appreciated by myself, Daveskee, El Glam-O, and the hot Russian MILF who needs me to fix her DW.

And please, Daveskee and I have both made certain that the drain lines are clear and un-kinked, the air-gaps are clean and/or new, the disposal KO has been KO'd etc, etc.

To daveskee: As a person who has remodeled and sold and repaired, I'd suggest you swallow the moral dilemma and go with Speedball1's answer: high-loop, hide the loop, and wait for the home inspection team to complain. If they do, offer the buyer the $ for the repair and nothing more. This "interesting puzzler" could cost you a sale.

Thanks for reading. I'll be interested in any further brainstorming.

Here's something (yet another thing) I learned by screwing up and messing around until I finally got it right. In the top of an air gap is an insert with two holes. Inside the air gap are two divisions. One division connects to the inflow side of the air gap (from the dishwasher) and the other connects to the outflow side (to the disposal). If the top insert is put in wrong, water will flow from it when the dishwasher empties. For correct operation of the air gap both holes in the insert need to be positioned over the outflow division of the air gap.