Hi. We built our house and know all the plumbing and drain details. We have lived here 4.5 years. In the last 6 months, we have had trouble with the toilets not flushing properly. They fill up to the rim, then slowly the level goes back down. Plunging helps it go down faster, but the problem repeats with each flush. Also, the toilets (and only the toilets) gurgle when the washer drains. We snaked the drain line from the outdoor cleanout as far as it would go. No significant clogs were present. Problem still exists. Our vents are in the attic. We thought maybe the vent cap was bad, so we removed it to inspect it. The toilets all flush beautifully without the cap on. However, a new cap did not solve the problem. There is no way for birds, etc. to enter our vent system. The tubs, washer, dishwasher all drain fine. Septic was cleaned out earlier this year and "did not need it really". We do not have issues with the tanks or field per expert inspection. We have a double tank system, gravity feed.

We have yet to try snaking from the inside out, or flushing the vents because we do not have the proper snake required. We do have an internal clean-out because of a sink we never installed and it is capped. It has always been this way. Currently we are removing that cap in order for the toilets to flush as we cannot keep the vent cap off (sewer gases would build up).
I can give any amount of detail as to the layout of the drains, etc. But we did not have problems until the last 6 months. Plumbing and sewer all doen to code, inspected. Sewer lines in slab. We are baffled.

The way I read your post, your vent terminates in the attic and there is some kind of cap on it. The toilets work fine with this cap removed. Can you post a pic of this cap or describe it.

Not sure how to do pictures, I can look into it if you still want pictures after reading my update. It is a typical vent cap, you can suck air through it but not blow air out of itn as long as it is verticle. We replaced it with a different kind and the problem persists. Both work fine if using your mouth to test it. The new one is a Sure-Vent by Oatey. Looks like a bullet or minaiture fire-hydrant. Has a disc sort of thing that slides up and down a little bit.

Update: So it is obvious that our system is airlocked and we think it may be the ice. We have about 2" of ice on the ground and the current problem started after the ice storm hit. We had a lot of freezing rain and the ground is already saturated.

Removing the outdoor clean-out cap also allows the toilets to flush and that is AFTER all the plumbing fixtures in the house of course. Removing ANY cap allows the toilets to flush.

I understand the vent system is like having water in a straw and as long as your thumb is over one end, the water will not come out. The vent works like removing your thumb from the straw. However...

Is it possible the system is airlocked from the receiving end? Like holding your thumb over an empty straw and plunging the open end into water, no water will come into the straw because there is no place for the air to escape.


SO does a septic field breathe?

We have decided that the issues we had in the last 6 months were unrelated. The issue was usually cleared up with plunging or running a tape in the sewer line. It may have come back a few days later but once we got a large clog out with the tape the problem did not come back until this week. This current problem does not get fixed with these options.

We bought a 25' snake to do the sinks but we have not used it yet as we think our problem could be an airlock on the receiving end. I can still run the snake down the vent pipes and through the sinks and washer lines and tub if you think that would help. It is definitely not getting enough air in some way.

By the way, the master bathroom has its own vent, but it still connected to the system and does not flush either. There are two toilets in all.

Never heard of some one using a AAV vent on the main vent. Theoretically it should work. Not sure if it is approved for main vent. If removing the AAV makes everything work, that pretty much narrows things to the vent not working as you would like. At least well enough. That may be the case. The vent is working but simply not allowing enough air in fast enough. You did not say how large the vent pipe and AAV are. If you think that the problem could be not enough air, remove the AAV, put on a "T" fitting, a couple 90 ells and put in two AAV's.

Two other things to consider, a 25' drain snake may not be large enough to clear a 4" sewer line. You may pass through a blockage and then have it close up on you after you remove the snake. May have to rent a larger snake.

The other thing is the present weather conditions. If you are on a septic system and the sewer pipe to the tank is close enough to the top of the ground it may be frozen. If the ground in you septic field is frozen down to the depth of the distribution lines you septic system will not work. If the water cannot get out, no more water can get in. Your present problems may be weather related.

I would at the least double up on the vent AAVs or run vent pipe through the roof. Why doesn't your vent go through the roof?

The vent line is 2". I did not use a snake on the sewer line, I used a tape (100'). The vent does not go through the roof because it was easier to vent it in the attic. The T is an idea, however, does not explain why both toilets do not flush when the one has its own vent and everything used to work fine.

Can you tell me what kind of vent cap is used? We were told to get the one we have by a licensed plumber.

The tanks are close to the top of the ground. We have had much colder winters than this without this problem, however, the ground saturation was not as much. Usually the heat from the tanks is enough to keep the ice thawed off the caps (lids) but not this time. I removed the ice from two of the lids this morning (salt water and gentle breaking). There are 3 lids but two tanks. We were never quite sure why there are 3 lids. We did not witness the installation of the tanks, only the fingers.

We have never had freezing tanks before. We do not have to dig to get to the caps. I can go remove one now and look into it.

Also a correction from my first post: there is only one attic vent.

Never though about where the air that is displaced by incoming water goes in a septic system before. It has to go somewhere. Only place where it can go is back up the vent pipe. Your AAV would not allow that.
Guess you are going through the roof with the vent pipes.

A different vent WOULD allow it? Again, please advise the proper vent type. I am curious why we were never told this before (like, when we were building this place).

Can you clarify a bit more? Do you think it is the ice causing trouble on the septic end and that is why our vent is suddenly inadequate? Can a septic become air-locked? I feel I am repeating myself and that my questions are not really being answered. I am just honestly perplexed, not angry.

Also, there is no air coming OUT of the vent when we remove the cap during a flush, there is only suction. Plus, if the water is pushing down the septic line, how would it go back up the opposite way to the vent? Wouldn't this cause some noises out of all the uphill plumbing fixtures? Thank you for your answers so far :O)

OK, lets say that when you flush a toilet 2 cubic feet of water flow into the septic tank. Therefore 2 cubic feet of air must flow out. If it does not, the air must will be compressed increasing the air pressure in the tank. As this is repeated the air pressure in the tank at some point, will prevent any more water entering the tank.
If the vent pipe is open the air will escape back up the sewer line and vent pipe. If the vent pipe is closed, the air can escape out the distribution lines. How fast depends on the soil type and conditions.

The vent pipe does two things. It allows sewer gases and odors to escape to an acceptable location. It allow air in to fill the void left by the flow of water.

With respect to the flow of water, a vent pipe is only necessary if the pipe is completely filled by the volume of water flowing down the pipe. If the pipe is not filled by the flow of water the air ahead the water and displaced by the water, can flow over the top of the water and fill the void left by the flow of the water.

Again if the flow of water completely fills the pipe, it must get air from out side the pipe behind the flow of water, therefore it must get air from the vent pipe.

Turn a coke bottle up side down, it gurgles because as the coke flows out, air must flow in. The coke is flowing in one direction and the air in the other. Tilt the coke bottle slightly and the coke can flow out of part of the opening and air can flow in the remainder.

AAVs are designed to do two things. One is to prevent sewer gases and odors from escaping into your house. The other is to let air in so that the water can flow down the sewer pipes.

There will be no acceptable AAVs for this situation. Its very design says don't let air escape. If it let air out it would not be doing its job of preventing sewer gases out. If it did it would just be an open vent pipe.

You said earlier that when washing machine runs the toilets gurgle. Gurgling would be like the coke bottle. Air is being drawn in to the system. What I suspect that you mean is bubbling. Bubbling would occur when air is forced out through the water. Washer usually dispense a large volume of water very fast.

Whether the toilets bubble or gurgle probably depend on whether the toilet is between the washer drain and the septic tank or the washer drain is between the toilet and the tank.

The bubbling or gurgling toilets and the fact that if you remove the AAV or open the clean out and the system works with out problems support the logic I have presented.

You ask why you weren't told this before. I ask, who told you you could use an AAV on a main vent? As I stated earlier this is something I have never heard of before. An AAV might work if you were connected to a municipal system because of the size of the system and because it is not a sealed system. It is extremely doubtful that it would be allowed though.

As far as answering your questions, I think I have. The solution to your problems is to remove the AAV and run the vent pipe through the roof.

Thank you, I have found a more appropriate answer elsewhere from someone who did not ask me questions I already answered (like who told me to use an AAV)and who actually answered the questions I asked.

I did not need a physics lesson from something I already explained to you that I understood. AAV's are acceptable. There is another (actually two) solution you did not mention that was nicely explained to me by someone else.

So much for help.

If you don't mind, could you tell us the other two solutions. Just curious. In my area aavs are not allowed to vent the entire house.

Yes.

You can add a vent outside in two places, the septic field itself (kind of hard to do after the fact but it CAN be done) or by the cleanout.

You can also run the vent out by other means than the roof (we have several reasons we are not going through the roof), mainly the same place we ran our dryer vent, through the eves out the soffit.

Just waiting for the ice to thaw will solve the issue, but who knows when that will be. Plus, don't want to deal with this in the future so we want to do a permanent fix in case it happens again.

We tried the T and it did not work.

Thanks for taking the time to answer my question. It truly is amazing how much codes vary from area to area. In my area, we are not allowed to terminate a sewer vent through the side of the house, only the roof(which is required). However, since its allowed in your area, the vent through the eve or at the outside cleanout or tank should solve your problem. Hope everything works out well for you. Take care.

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Originally Posted by homeowner2003

So much for help.

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Well, I am truly sorry that I couldn't provide you with an answer that you liked. I am happy someone else has been able to do so. You plumber told you, probably at your insistence, that you could block the vent pipe with an AAV. But then, that didn't work did it?
I have to ask though, if you are only going to accept answers that you like, why do you bother asking, why waste other people's time, just do what you want.

Way to make incorrect assumptions. If you are only going to answer people that will believe whatever you say without question and slam them when they don't, why are you answering questions? So I am just supposed to take your word for it and not question it? That is theoretically what got us into this mess to begin with, we trusted our plumber. We did not insist on anything. He is the one who told us there is not need to go through the roof. He is the one who suggested the AAV. He is the one who told us it met code etc. Turns out he was right.

I asked you twice what vent to use instead of an AAV and you never gave an answer. You just kept saying go through the roof. Great. Go through the roof. AND USE WHAT KIND OF VENT ONCE I AM THROUGH? I asked you if a septic can become airlocked. No answer. You told me using a 25' snake was useless on the sewer line when I had stated before I used a 100' tape. All this made me distrust your answers, like all you could see was how stupid we were for venting in the attic and that until I was willing to go through the roof you had nothing further to say. So I am stupid for following code, I am stupid for having it inspected and trusting a licensed plumber.

You never even tried to answer several of my questions, yet you claimed you answered them. Well, anyone can go back and read and see that was not the case. When you started being evasive about answering my questions, I began to doubt the answers you did give. Why wouldn't I?

You act as if this problem was my doing, like I refused to do it right and now I want a non-kosher answer to fix it. I told you (gee, I am repeating myself again) that a licensed plumber advised us and that it was inspected and passed inspection. So if it was so wrong and the legal authorities approved it, what does that say? Who AM I to trust? Well it turns out it is not wrong, that the freakish weather has created a temporary issue that needs to be fixed. Nothing in our house is "illegal".

So whatever. You will think what you want, I will think what I want, right? That cannot be changed. Make whatever assumptions you want, that does not make them fact. If slamming me makes you feel better about yourself, knock yourself out.