Please critique this drain configuration!

Hi all!

Need to re-plumb this drain assembly under my vanity. There used to be a simple S trap. It used to drain slowly due to improper venting (more specifically, there isn't one.)

I want to change it to a P trap and add an AAV (I know, sometimes frowned upon, but better than nothing I think.)

Anyway, here's what I've come up with. Is this acceptable? My apologies if this turns out to be a ridiculous solution!

Thanks!

Had to look at that twice before answering. It is........Ok but honestly, you would have been better off leaving the S trap than going through all that piping and now you have an AAV added also. S traps are not legal to install new, but you can certainly repair an existing one. That arraingement will not drain any better than the S trap did.

Thanks, Wally. The reason I decided to change it was b/c of what I read of the effectiveness of a P trap vs. an S trap...not the effectiveness of draining water, but of trapping the gasses. I know I didn't HAVE to change it, but I wanted to do it the best way. The only way I could fit a P trap was to route it out and then back down again.

I thought the poor draining was due to inadequate venting. Are you saying the AAV valve is pointless in my application?? There isn't a vent stack anywhere near this fixture.

Everything is still dry-fitted, so it can be changed. Thanks!

If it's not draing well, adding a vent is not going to fix that situation. Vents don't cause drains to drain faster or better, they protect the trap seal from siphoning. I suspect that you probably have a blockage in the drain somewhere. don't get all hung up on whether or not an S trap is good or bad. My house is a couple hundred years old with most of the original cast and galvy dwv piping. Not a p trap in the whole place. It drains fine. Occasionally one of the s traps will siphon and so you run a little water down the drain to re-seal the trap.

If the cause of the poor drainage is because you have an "S" trap, then an AAV is NOT going to improve the situation. You have to find out WHERE the drain is obstructed, and it does not necessarily have to be in THAT sink's drain, and unplug it. Once you do that, if the drain gurgles after it drains THEN an AAV will cure THAT symptom.

Thanks guys. I think I'm starting to understand.

If I'm reading this correctly, the setup in the picture has to be as good as or better than an S trap, right? Should I go ahead and hook this up and test it? If I still have slow drainage, then I'll KNOW it's a clog somewhere. If everything is fine, I won't necessarily know whether I need the AAV or not, I suppose. Is it ok to leave it there? Can an AAV do more harm than good if it's not absolutely needed?

Nevermind! I decided to try an S trap. There must've been a clog in the old line to the floor. It drains just fine, and I don't hear any gurgling at the end. I guess everything is ok.

Thanks a lot for your help guys!

If there were, you should have been able to SEE it. It is academic now, but if the sink drained with the AAV removed and didn't with it installed THAT would have told you that the line was plugged. And, your design for installing the AAV would have to qualify as one of the most difficult, elaborate ones ever.

hj said:

If there were, you should have been able to SEE it.

Click to expand...

You know what? I didn't even look. My concept of venting was obviously off, so I wrongfully assumed that was the problem. When I started remodeling this bathroom months ago, I simply ripped out the drains to remove the vanity and didn't even check if there were obstructions. In the meantime since tearout, I have plunged a shower drain. It's quite possible I cleared the obstruction then.

hj said:

It is academic now, but if the sink drained with the AAV removed and didn't with it installed THAT would have told you that the line was plugged.

Click to expand...

I never actually tested it with the AAV installed. After reading this thread, and before gluing the connections together in the pic, I decided to just try it with a new S trap. Sure enough, it was fine. So, the convoluted mess in the pic never even got tested.

hj said:

And, your design for installing the AAV would have to qualify as one of the most difficult, elaborate ones ever.

Click to expand...

So if I'm reading correctly NOW, my report card looks a little something like this:

Effort - A
Creativity - A
Knowledge - F

In the end - despite wasting both time and money - I learned a few things. Thanks again to you and Wally!