Can someone tell by looking at my photo if there is something wrong the way I configured this vent? It is a double sink with a garbage disposal and a dishwasher drain. It drains very slowly and water backs up into both sinks. Basically the same thing it was doing before I installed the vent. The drain line is 2" pvc into a 2" galvanized pipe in the basement floor. I assume that goes into the cast out to the street. All other drains in the home work, bathtub, toilet, bath sink, and basement sink. I would expect that as they are all vented out through the roof stack. The kitchen sink is not. I have snaked the pvc and galvanized line, so not clogs.

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the san tee is going the wrong direction but should that make a difference ?
does it drain any better with the studor removed?

I did notice I put the San tee on wrong. Was not sure if it mattered as far as airdraw. It works great when I lossen the vent. I can hear it pulling air around the threads.

The sink doesn't need a vent to drain. The vent keeps the water seal from getting sucked out of the trap. There's a blockage/belly in the pipe. You might be hearing displaced air coming out from the drain.

okay thanks everyone. i will investigate further. I am not sure where the clog would be. I have a clean out where the pvc and galvanized pipe meet. i rig up that opening so i can pour in a five gallon bucket of water and it takes it all with out any problem.

if i remove the Studor vent the sink drains as fast as i can add water. maybe if a run a vent stack to the outside that will be the ticket. probably easier said then done in this house.

if it drains w/o the studor but not WITH the studor as you say there are two possibilities

1) vent is 'broke' and needs replacement (not opening - not allowing air to enter upon a NEGATIVE drain pressure)

2) downstream stoppage which is 'relieved' with FULL BORE air inlet (such as a conventional piped dry vent)


this is a typical issue with AAVs which only admit RESTICTED air flow at best making ANY minor downstream obstruction evident

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

Thanks I have tried a different vent with the same results. I understand what you are saying that it may need a dry vent,which is basically what I am doing when I remove the Studor vent, all be it that sewer gas is venting under my sink. This then allows enough air draw for water to flow if there is a restriction downstream. I have attached a diagram of the line. I do not know what happens once it enters the floor. There is a cast stack in the basement that the bathroom fixtures use. Like I said all those work fine






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keep the studor vent on tight. remove the plug from the cleanout. hold a big bucket under the cleanout and let a full sink of water go. let us know what happens.

Another possible problem, but not related to the poor drainage, is that it appears to be a 1 1/2" draun not a 2" one.

thanks Packy I will remove the cleanout at the basement floor where the pvc connects to the galvanized pipe.

You are saying tighten the Studor, fill the sink with water open the drain and observe the flow.

If there is blockage in pvc section of pipe I should still see slow drainage. If it flows normally the blockage could be in the galvanized pipe at some point under the concrete.

One other thing i did try was: tighten the Studor and losen the cleanout in the basement ceiling. I did not remove it entirely just enough to see what would happen. It immediately starts drawing air thorough the loose threads. Again acting as a vent.

Also, I can run the sink faucet for a while, maybe 10 seconds, before it starts to back up.

What is the life expectancy of galvanized pipe under a concrete floor? Maybe my problem is in that section of pipe. I did however snake it.

This is all at my sons home and I am a few hours away so I will need to try these things next time I am there.



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what size snake head did you use into the 2" piping?

it is strange that with the studor vent removed you get good drainage ????

I used a 25' hand crank drum snake. I would say the head is no bigger then 3/4 inch. I believe if it is piped correctly, then there must be enough of a restriction in the drain pipe somewhere causing the AAV not to work properly. The system just needs more air to drain.

I will try to snake it again maybe rent a bigger snake to use on the galvanized section. If there is a problem it's probably there.



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I think if your AAV is acting up like this it's not the vent malfunction but your drain. The AAV simply magnified your restriction issue. With the AAV on it only let's air in, not out, so any positive pressure created when met with resistance from a downstream clog will back up because the air has no where to go.

By removing the AAV if your flow is not a full flow filling the entire pipe, the positive pressure finds an outlet to push air out to allow it to go down further. If there is another vent downstream of your sink and upstream of the blockage you will also be able to drain and that vent would have hid the problem for a while in a similar manner. I say your blockage is downstream of your sink, but upstream of the next vent.

A 3/4" snake head may not be enough. The blockage, especially if from a kitchen, could be accumulation of grease, cheese, pasta, rice, coffee grounds, and who knows what else all "geled" up at a 90 degree elbow, a messy gluey gummy swollen blob of soft blockage and when your 3/4" snake hits it, it just poked right through and made a small hole, and kept on going forward. This allows you to drain a bit, then a day later the mess moved down a few inches and seals off again. Perhaps a larger head snaking it more thoroughly, with water running as you snake so the loose debris would rinse down as you break it apart, would do the trick?

Not a pro just a DIYer.

if you can get the hand snake in for its full length, do that. take the end out of the hand spinning part and put it into a 1/4 inch drill. be careful. so with a foot of the snake wire sticking out of the cleanout, run the electric drill. slowly at first and gradually increase the speed again, be careful. once you get the feel of the snake wire spinning you can pull it back and forth while it is spinning. run water as it is spinning to wash debris down to the big pipe. you want that wire bashing around inside the pipe so it knocks loose as much debris as possible.