I upgraded an old laundry sink recently. The 1.5" drain goes into the basement slab (to a recently jetted main sewer line). The above-ground was changed to new PVC, sanitary tee to the laundry sink p-trap, then up to about 50" or so where there's an AAV. Looks pretty and plumbed nicely.

Started off with an ABS 'cheater' vent.


The drain now drains slowly. It does drain, but very slowly. As soon as I removed the vent, draining went back to normal fast draining.

I figured it was the cheap vent I chose, so upgraded to a Studor Redi-Vent


Same problem. It doesn't drain well with the AAV. Remove the vent - and it's all good.

What's next? I can't figure out why the AAV isn't working as it should. Thanks in advance!
-Mike

 

I'm still having this issue, and short of completely removing the AAV, I'm stumped. Open pipe, sink drains perfectly. Screw in the AAV, sink drains really slowly. Any thoughts or suggestions?

 

I'm not positive it will fix the problem, I think so. Instructions for an AAV state the mark/line should be 6" above the top of the trap line.
I would say the vent is too high.

 

"Must be located at least 6" above the trap arm."
They give you an "at least" but not a maximum.

 

The fact that the pipe drains when the AAV is removed tells you the AAV is not working.
I have the exact same set up in my garage and the vent works fine at 6".

 

I'm not arguing. They should specify that an extended length will hinder the performance. Something like 6" minimum and not over 15".

 

Very true.........................................

 

The vent is not for draining purposes. The vent is so the trap does not get siphoned when other fixtures are used.

Think about it. Without a vent the fixtures will drain as the drain itself works as a so called bent.

I mean look at a toilet vent... Take the toilet vent away and the toilet will operate the same without it. The vent on the toilet is so other fixtures dont siphon the water out to release sewer gas..

I can probably bet if you drop that trap and snake that line to the main your issue will go away.....

That could be a shallow pitched line running under the slap to the main..

Plus laundry line means lint build up. Especially where the y meets the main under slab..

Just my opinion from my experience...

terrylove.com

 

I will try that... BUT - the part that is driving me crazy is that when the vent is screwed in, I can hear the water literally dripping down the vertical part of the PVC, like a just barely running tap.

Unscrew the vent, and woosh - drains as fast as you'd expect.


Thinking about it more... maybe you're right Mike. A partial clog is just blocking it enough to fill the pipe and start a vacuum, thus causing the slow drain. But it's not enough of a clog to actually slow down the draining of the water on its own.

Ok, fine - you've convinced me to snake the branch. I'll let you know how it goes.

Thanks!