Wet venting tub, toilet and basin (can I add an AAV)?

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yousonso

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Hey there folks. First time to the forum. I had a remodel done where I added a tub to my bathroom system. The toilet and tub are wet vented to the basin, which has the dry vent. The issue I have is that when the toilet is flushed (only certain times), the tub has a gurgling noise. I think the wet vent setup is syphoning from the tub's P-trap. Running water remedies the noise... I don't let it get too bad (meaning there has been no odors).

To permanently remedy this and to avid the occasional running of water in the tub, can I increase airflow or prevent the negative air pressure somehow by adding an AAV to the basin after its p-trap? I know the right way is to vent the tub, but everything is in cement (tiles are in place) and I'm out of money.

See images below to hopefully better explain my dilema.
IMG_5372 copy.jpg

IMG_5373.jpg
 

Tuttles Revenge

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To me it sounds like something isn't installed correctly for a horizontal wet vented system. The dry vented fixture should be upstream of all but one fixture in the series. Toilets should be downstream (tho some codes have exceptions for that). If the toilet water is passing by the tub trap arm and causing an issue, it is either pushing water up.. or sucking water down and I suspect its sucking as the toilet line is filling the horizontal drain, which it shouldn't be able to do.

I've set up horizontal wet vent systems in our parking lot to diagnose a similar issue that we had at a customers home and no matter how badly I installed the system to block all the vents, I couldn't get it to fail until I clogged the downstream drain and caused there to be no place for water to go.

Adding a AAV to the tub trap arm might alleviate the issue, but I doubt that any other location would accomplish this. What sort of tub do you have installed? Alcove, drop in or freestanding? Most tubs have a Lot of dead space underneath of them which could be used to add a vent.
 

yousonso

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To me it sounds like something isn't installed correctly for a horizontal wet vented system. The dry vented fixture should be upstream of all but one fixture in the series. Toilets should be downstream (tho some codes have exceptions for that). If the toilet water is passing by the tub trap arm and causing an issue, it is either pushing water up.. or sucking water down and I suspect its sucking as the toilet line is filling the horizontal drain, which it shouldn't be able to do.

I've set up horizontal wet vent systems in our parking lot to diagnose a similar issue that we had at a customers home and no matter how badly I installed the system to block all the vents, I couldn't get it to fail until I clogged the downstream drain and caused there to be no place for water to go.

Adding a AAV to the tub trap arm might alleviate the issue, but I doubt that any other location would accomplish this. What sort of tub do you have installed? Alcove, drop in or freestanding? Most tubs have a Lot of dead space underneath of them which could be used to add a vent.
Thanks for your reply. I also suspect its sucking from the tub trap (as the noise sounds liked a suction). Adding water to the tub stops the noise in the tub. I have a freestanding tub (with jets and whirlpool). I thought maybe adding an AAV at the tub drain may be an option too... it just would require me lifting off the tub and then examining how much was concreted and tiled under there. I hope there is access... the easiest access for an AAv was under the sink (hoping it would improve the system with an added vent). Thanks again for your reply.
 

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It would help to know the layout of each fixture and its location or sequence in the piping system. Typically the sink is already the location of the vent for a horizontal wet vent system, so adding venting there would be redundant. Unless they piped it differently. We don't know. The thing we do know is that the tub is being siphoned and the way to break a siphon in a plumbing system is to introduce air at the trap being siphoned.
 

yousonso

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It would help to know the layout of each fixture and its location or sequence in the piping system. Typically the sink is already the location of the vent for a horizontal wet vent system, so adding venting there would be redundant. Unless they piped it differently. We don't know. The thing we do know is that the tub is being siphoned and the way to break a siphon in a plumbing system is to introduce air at the trap being siphoned.
Sorry. All I have is the diagram I provided at post.
 

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If your sinks trap is vented to atmosphere/to the roof via a common vent, then adding a vent to it or near it likely isn't solving anything. If the toilet is drawing a siphon against the tub drain, then protecting that trap with a way for air to enter is likely the only way of solving your issue.
 

yousonso

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If your sinks trap is vented to atmosphere/to the roof via a common vent, then adding a vent to it or near it likely isn't solving anything. If the toilet is drawing a siphon against the tub drain, then protecting that trap with a way for air to enter is likely the only way of solving your issue.
Thanks for the response.
Update: I managed to contact the contractor and felt he is confused of how the air can be siphoning from the p-trap at the tub. He asked me to recreate the noise or allow it to happen again (don't refill with water) and when it happens again to get a piece of toilet paper and dangle it over the tub's overflow to see whether or not the paper is being sucked or blown out.

I did go up on the roof to check the vent stacks and nothing appears obstructed. Ran a water hose and no issue or leaks.
 

yousonso

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If your sinks trap is vented to atmosphere/to the roof via a common vent, then adding a vent to it or near it likely isn't solving anything. If the toilet is drawing a siphon against the tub drain, then protecting that trap with a way for air to enter is likely the only way of solving your issue.
Could a clog of some kind in the drain also be the culprit?
 
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