Well I finally got the downstairs power room completed and the fixtures installed yesterday. I'm sorry I didn't snap a pic of the old drain piping because it was quite a mess. I installed new drains and thought I would have a much better performing setup, until I flushed the toilet and it wouldn't!

When you flush the toilet, the bowl just fills up like it's stopped up. Unscrew the AAV when the bowl is full and nothing happens, it just sits there. Flush with the AAV removed, and it works fine. You can feel a blast of air coming out of the vent when the toilet is flushed, followed by air being sucked in.

The AAV is installed in a vented access box like this in the wall above the sink. The idea is that one I hang the mirror over the sink you won;t see the box.



Here is the setup:



Here is another pic showing how the 1/2 bath was added into the main plumbing years ago. They basically repurposed the old cleanout, and added a 2nd whole house trap, but no foundation vent.




I'm thinking I need some sort of second foundation vent since I have a second whole house trap? All the walls are closed now so extending the AAV vent line up through the roof is not an option, eben thoiugh that would p[robably be the best solution.

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Not a plumber by trade but a fierce DIYer



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If the bathroom you are experiencing the problem is piped upstream of the PVC whole house trap on the left side, then I think that trap is causing problems for you.

Do you need that trap? If all the fixtures are individually trapped in the bathroom you don't really need that trap...or is it code required where you are?

When you flush the toilet the water evacuating the toilet will create positive pressure ahead of it and negative pressure behind it. That positive pressure meets the water in the whole house trap and has no where to go. It can only try to go through the AAV which it can't, or it can create bubbles in the sink trap. This inhibits the flush action. The AAV can deal with negative pressure but is designed to not let through positive pressure. A clog downstream can have the same effect.

As a test to see if the whole house trap is your culprit, open that CO and shop vac the water out of the trap and reflush with AAV on. If that flushes fine you have your answer.

AAVs are designed to let air in, but NOT (repeat NOT) out.

Else sewer gasses would be vented as well as air.

Your toilet may be airbound.

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

It is not a question of whether it "may" be airbound. There is absolutely no question about it. The house trap has created a toilet with a "double trap" which cannot flush. There would be no problem IF he had used a vent through the roof instead of an AAV, but he used the "quick and dirty" method and now he has to correct it.

No question about it hj! The problem is I cannot extend the vent through the roof because the walls are finished, so the question is HOW else can I fix it?

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Not a plumber by trade but a fierce DIYer

Remove the whole house trap, `

Unscrew the AAV, tied a 2" flexible tubing to that pipe end and run that tubing out the window!

No seriously if you cannot put in an atmospheric vent up the roof, can you drill a hole through the wall where the AAV is and connect to the pipe end a 45 and take it outside the house, then another 45 to run up the exterior wall to above the roof line? That may be ugly to look at outside and probably not to code but it would work theoretically.

Curious, does the 2" line above the 3" have an atmospheric vent upstream of it? If so you can reconfigure the piping and tie the 2" into the 3" just upstream of the whole house trap. That would allow air to escape from the 3" into the 2" and out its atmospheric vent, and eliminates the negative slope segment in the 2".

Or get rid of the whole house trap.



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Don't laugh, but that 2" line goes to the kitchen sink where there is another AAV. I think the whole house trap has to go. Time to grab the sawzall.

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Not a plumber by trade but a fierce DIYer

It would still work and would also be completely against code, because unless it rose a "long way" above the mainline it would violate the "connect above the highest fixture" rule and create an "alternate drain path' in case of a stoppage.

From the looks of the trap fittings there, it looks like you’ll need to take it back all the way to the cast iron and pipe from there... no space to just cut and re-glue...

I took the trap out yesterday and here is what we have now. I reinstalled the AAV in the powder room and the toilet flushes great! If there were to be a back up from the sewer, it would go out of the foundation vent in the pic, that's the lowest point and below any of the fixtures.



What you can see in the pic is the last of the cast iron left in the house. It transitions to PVC going upstairs, both bathrooms upstairs have been re-plumbed and the stack is now PVC. On the other side of the foundation, it goes to green SDR out to the street. This piece needs to be redone by a pro so that everything ties in upstream of a single whole house trap and foundation vent. Right now it's not up to code because the 1/2 bath bypasses a whole house trap. A better way to do this would have been to add a second foundation vent but no room for it.

Interesting about the PVC that's there, they must have either failed to prime or used the wrong glue, because some of the joints just came apart like they were never glued. They never leaked though. The wye coming off of the CI wye is really in there, so I was happy when the homemade P trap came right out of there. I primed, wiped down the pipe, and primed again before gluing and it seems solid now.

The angle I needed was 30* and it seems that nobody makes a 30* elbow, so I was able to use a 45 a pair of 22.5's to get where I needed.

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Not a plumber by trade but a fierce DIYer



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