# AAV or Studor Vent Needed for this Tub and Shower Drain?



## BillyDIY (Aug 24, 2008)

My main 3 inch drain stack runs through my garage and up along the far wall. The first side connection is a 45 degree 2 inch that then 45 again so that it looks horizontal (minus the req fall) cuts across and then 90 straight up 90s over to the P trap of my shower drain. Back to the 3 inch waste in the garage this proceeds to my garage ceiling does a 90 across the ceiling about 3 feet to the master toilet where it T and then behind the toilet it 90s up behind the toilet wall and up into and out the roof. Take a look at the attach image. It is not to scale but gets the gist of this.

So my assumption is that since my shower drain is effectively the first branch albeit 45 degree that some sewer gas could be going up it? I understand the p trap should be stopping it, but maybe when water goes down the drain or flush a commode, etc that it allows it to escape.

Should I or am I required to vent this any more? Can I or should use an AAV or Studor Vent? If so, where exactly should this go?

More Background 
Replacing a shower alcove in my master bath. Since I didn't tackle this project in a weekend it has dragged on for quite some time. During tear down of the existing ceramic I plugged the drain in the shower and it stayed plug for at least a week. When I unplugged it recently it reeked. I have since poured a number of buckets of water down the drain and it doesn't smell nearly as bad, but if you put your nose right against it you can still tell there is a smell. When the shower was in operation there was maybe less than 1/2 dozen times in six years that I smelled anything so there is certainly not a phenomenom there. Since I have the bathroom gutted and I don't want to regut it if I later find a problem or if my layout is a code violation or something I investigated further.

My house was built in 1979 if that matters.


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## Nestor_Kelebay (Jun 17, 2008)

It's hard to follow descriptions, but if your plumbing is similar to that shown in your drawing, then the Studor vent would go immediately DOWNSTREAM of the P-trap.

It's easy to understand where a vent pipe or AAV should go if you understand what it's for.

A subway leaving an underground subway station can suck air into the tunnel behind it, creating a strong wind in the subway station. In exactly the same way, water draining down a drain pipe can create a suction behind the draining water. That suction could potentially be strong enough to suck the water out of a drain's p-trap. If that were to happen, then sewer gasses could subsequently come into the house through that empty p-trap.

The whole purpose of a vent pipe or an AAV is to allow air to rush into the drain pipe behind the draining water so that you never have suction behind the draining water that could threaten to suck the water out of the p-trap.

It's just as simple as that.

So, you want to install your vent or AAV as close as conveniently possible to the P-trap. You can check with your local plumbing inspector to see if the plumbing code requires that the vent pipe or AAV be within a certain distance of the p-trap.


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