New to the forum and I am impressed with the content. I have looked everywhere on Google and this and other forums, for an answer to my problem. I have a 5 year old bungalow on a septic system that has an absorbent well instead of a weeping field. We have been experiencing a sewer smell in our living room when ever laundry is done. No smell ever, in the laundry room. The following is what I have noted so far: 1. the toilet bowl level will drop when laundry is done. 2. the bathtub drain will gurgle when the washer pumps out. 3. have installed an Oatey 20 DSU Air Admittance Valve on the washer stand pipe, 4 " above where the washer discharge hose enters the stand pipe. 4. waste line is 1.5" with a P trap at the bottom of the stand pipe, and the vent line branches off right after the trap.
We have a Maytag washer, that discharges at 23 USGPM, and I read in another thread that this may be too much for the 1.5" waste line. Also read that the laundry should have its own vent stack to the roof. I have not seen this anywhere on any other houses. I can do this, but it would be a big job, and I am hoping there is another solution.
Any ideas will be gratefully accepted

The "gurgle" tells me that you have a vent problem, (perhaps two). I would snake out the lavatory roof vent line since it would appear that the washer's
Attempting to wet vent through it. If the Oatey AAV's installed on the stand pipe ahead of the trap and not on a vent pipe behind the trap then it's doing no good. The open stand pipe serves the same purpose If I understand you correctly then you are discharging your washer into a unvented trap. This should be corrected and the situation checked again. Regards, Tom

Thanks Tom for your quick response. I need to clarify a couple of the items you mentioned. I can certainly snake the vent stack to check for a blockage and since there is no snow on the roof, I may do that today. Hooray for mild winters! Regarding the placement of the Oatey AAV, if I understand your comment, I should install it on the vent pipe that is connected downstream of the trap, that then goes up to the attic and then over to the main vent stack. This is probably a dumb question, but where should the vent line connect to the waste line, before or after the trap? In my house, the washer drain pipe is 36” above the floor, drops straight down through the floor to the basement ceiling where the trap is located, and the vent line T's into the waste line about 6” downstream of the trap. If this arrangement needs to be modified, I would appreciate your thoughts. If the washer stand pipe is vented as I described, (or as you might suggest) then the Oatey AAV is not really required is it?
Lastly, my main stack is a 3” black plastic pipe that exits through the roof. Due to potential heavy snow build up where I live, it extends about 2 feet above the roof line. Very mild now so frozen vent is not the problem. I have a 90 degree elbow on the top of the stack to prevent leaves from falling into the stack. Does that elbow cause any problems? Should I remove it?
Thanks again, Ralph

"where should the vent line connect to the waste line, before or after the trap."
I have put up a rough drawing of the average washer trap and vent.

"the washer drain pipe is 36” above the floor, drops straight down through the floor to the basement ceiling where the trap is located, and the vent line T’s into the waste line about 6” downstream of the trap."

Ya lost me with the "vent line tees into the waste line." Is there or is there not a separate vent on the washer that you've connected into the waste line? Or didi you connect the washer trap into the waste line. Either way it doesn't smell good to me. If the waste line services anything upstream from the washer trap then you can not connect a vent to it and if you've connected the washer trap directly to the waste line then you have left it unvented.

"I have a 90 degree elbow on the top of the stack to prevent leaves from falling into the stack. Does that elbow cause any problems? Should I remove it?"
No, most people screen the roof vents to keep out leaves and critters but a 90's acceptable and should cause no problems.
Good luck, Tom

Thanks again Tom for your reply. Having read your reply, I am wondering about all of the vent system in my house. Your diagram for the washer waste/vent hook up is not at all the way mine is plumbed. There is nothing up stream of my washer. The way all items are vented in my house is as follows: drains drop though the floor to basement ceiling with a trap just below the floor, i.e. Bathroom sink, shower, tub, and laundry (except kitchen sink which has a trap directly under the sink). Each item drains to the main via 1.5” black plastic pipe. Just after where the trap empties into its waste line, there is a T and the vent line is connected there. Each vent line goes up to the attic and travels to the main stack that goes through the roof. If this is not correct, can you advise or direct me to somewhere that describes how the vent system should be plumbed and how it is supposed to work.
Thanks to all for time spent on my problem

Your 5 year old bungalow must have been plumbed by the owner with no inspection or C.O. You are vdescriubing "S" traps which have been outlawed for years in all of the states and Canada. A installation that is code uses "P" traps and vents off the tee,(see image). Years back we used "S" traps until the problems with them grew so great that they were outlawed. While you indicate vents they are installed wrong since it's impossible to vent a "S" trap by code. If I were in your shoes I would get a sharp plumber to come out and take a look at my drainage and vent system. Even if you don't do anything to correct the situation you will at least have the knowledge of what should be done. Good luck, Tom

Tom, Thank you so much for all of the time spent on my situation. You have given me all of the info I need to correct the venting system. By the way, I said P traps when I should have said S traps. The diagram you provided will allow me to properly inspect and modify my vent system. Thank you for that. I will have a plumber check out the entire waste system and make the adjustments, including a separate stack for the laundry room.
I guess I shall consider this thread complete now and write back to tell you how the system performs when the changes have been completed. Due to weather here in Eastern Canada, it may not be completed until spring.
Thanks again, Ralph :)

You're welcome Ralph,
Let me know how you make out. Regards, Tom