Replaced Vent with AAV - Mistake?

[the_tool_man]

Hi all. First post. So go easy on me!

Our house has its kitchen sink in a peninsula. It is a double-bowl unit, with a disposal on one side. Each side has its own p-trap, leading to a common waste pipe. Here is a photo I took of the old arrangement during a later remodel:



Last year, the drain clogged. I cleaned both traps, to no avail. I soon realized, due to the design of the waste piping, that there was no way to snake the drain from above the floor. So I went into the crawlspace, and discovered to my horror that the vent pipe for the sink was simply turned down through the floor and left to dump the overflow on the ground. I knew there was a problem as soon as I opened the crawlspace door. The smell was indescribable. Thankfully, I put down plastic years ago. So cleanup wasn't as bad as it might have been.



So, during a remodel of the kitchen some time later, I cut out the old plumbing and installed an air admittance valve. I also added a cleanout for good measure.



Everything worked fine most of the time. But, if we went a while without using the disposal, and then turned it on, it sent a slug of water shooting out of the other sink bowl. Understandably, my wife was not happy getting shot in the face by a geyser of dirty sink water. Looking at the last photo again, you can see that the two drain legs enter the main waste pipe directly across from each other. I reasoned that the momentum of the water was carrying it across and pressurizing the other side. So I cut out all of that and replaced the sanitary tees with wyes, offset from each other, to direct the flow downward (sorry no photo). However this made no difference.

Now I suspect the AAV is the problem. As I understand it, it won't allow sewer gasses to escape. So it must be allowing a pressure buildup when the disposal is activated. If so, this pressure might be causing Old Faithful.

So now I don't know what to do. I don't want to replicate the old arrangement, and have another under-house toxic waste spill. And I don't want sewer gas in my kitchen. I could install a vent in the wall. But I don't want to tear out part of my new kitchen.

Any other ideas?

Thanks in advance,
John.

 

[frodo]

2 x 1 1/2 x 1 1/2 x 1 1/2 double fixture fitting

instead of a

2 x 1 1/2 cross

 

[the_tool_man]

Thanks, Frodo.

I appreciate your guidance. But, since the last photo was taken, I've already replaced the cross with a separate connection for each side (sorry if that wasn't clear). The disposal leg intersects the main waste line several inches below the other leg, and points pretty severely "downstream" (I'll try to take a photo tonight). If it was purely momentum of the water slug causing the geyser, I would think this would have cured it. Another thing to consider is that the original arrangement used a similar cross fitting (see first pic) and didn't have the geyser issue throughout over 20 years of use.

What would you do with the vent if this were new construction?

 

[frodo]

Thanks, Frodo.

I appreciate your guidance. But, since the last photo was taken, I've already replaced the cross with a separate connection for each side (sorry if that wasn't clear). The disposal leg intersects the main waste line several inches below the other leg, and points pretty severely "downstream" (I'll try to take a photo tonight). If it was purely momentum of the water slug causing the geyser, I would think this would have cured it. Another thing to consider is that the original arrangement used a similar cross fitting (see first pic) and didn't have the geyser issue throughout over 20 years of use.

What would you do with the vent if this were new construction?

if it was me?

 

[the_tool_man]

Frodo:

So if I understand your sketches, I'm to use a loop of pipe for the vent, just like before, but hook the other end back into the waste line? I see how that means the overflow will end up in the sewer. But is this still a vent if it can't vent to atmosphere? I don't see this arrangement in my (old) code book. I'm in South Carolina, if that matters from a legal standpoint. Not questioning your wisdom. Just trying to learn. Thanks!

 

[frodo]

look under island venting / combination waste vent

you are using the top half of the drain pipe as the vent, the bottom as the drain


it is better than a av

 

[KULTULZ]

Maybe these will help visualize the concept-

 

[the_tool_man]

How important is the vent stack shown in those pics? I've found a few references that say it's optional. For me, adding that vent will be very hard to do, since it would have to go into an exterior wall.

 

[Mr_David]

Instead of using 2 trap arms, why not use just one?
Have the disposal ell discharge down into the p-trap.
Connect the 2nd sink with a santee between the disposal ell and p-trap.

The ABS one in photo has a wye and a cleanout. I added a 1/16th bend so I can run water after I clear the drain so the water does not trickle out as I retrieve my snake.

 

[KULTULZ]

The ABS one in photo has a wye and a cleanout. I added a 1/16th bend so I can run water after I clear the drain so the water does not trickle out as I retrieve my snake.

...scribble...scribble...

Another great idea!

 

[Mr_David]

...scribble...scribble...

Another great idea!

I install wye clean outs on the trap arms when ever I can.
I Work on a lot a properties that have repeat stoppages .
When I install the run of the wye on a trap arm I roll the branch of the wye up a little and plug it.
Makes that after hours stoppage quick and easy.