In Double Vanity Drain Challenges

[ngmtl]

Ran into a couple issues while testing out the drain configuration I came up with for a double vanity retrofit (Note: I had to make the decision early on to split the waste line in the vanity as opening up the plumbing wall to get dedicated lines into the stack was not practical [shared wall with another condo and building utilities]). Aware of code and potential siphoning issues, I opted to install air admittance traps under each basin [which NJ code makes provisions for in situations like this]).

Challenges:
1. Slow draining of the left sink (sink closet to the tie-in), especially if both sinks are in operation. Also get a slight gurgle in the right drain when using the left sink, it doesn't bother me but didn't expect it would occur with the extra air admittance designed in. The nature of the slow draining seems to be more of a siphoning condition. I don't suspect a clog and there should be plenty of gravity and slope to keep the water moving (1/4" per foot slope if not double that from the right sink, however, the trap on the right sink is lower than the left). The one thing a bit suspect in my design that I don't see a way around (no pun intended) is a 180 needed to get from the left trap into the tee.

2. Left side also has a slight leak where my drain and tailpiece (Price Pfister washer type, not supposed to need putty) are supposed to seal with the sink. I think I know what's going on with that - the vitreous China sink has some imperfections in it (small cracks and bumps). Right side is the exact same configuration with no leaks there. Open to ideas (silicone, putty, Flexseal ).

Pics:

And the basin defects working against my seal (basin is epoxied in, replacing would be less than desirable at this point).

 

[Terry]

1) Not what I would have done, but I also don't see that it would drain slow either. Assuming all the drains, including the ones in the wall are clear.

2) It looks to be a bad lav basin casting. Short of replacing the lav, Silicone may be the fix.

 

[Sponsor]

 

[ngmtl]

Thanks as always Terry!

1.) After looking and testing again, I think the drains are performing well enough. It's only if I turn on all four faucets at the same time, such that the supply exceeds the rate of the drain and the sinks fill up, that the left lav drains particularly slowly. Even in that worst case scenario, it still drains within a minute of shutting off the water. With one sink at a time, maybe even one and a half the drain seems to keep up in real time. I should note that our water pressure is also strong.

2.) Yep, enhancing the under washer with silicone made a nice bead, no more drips there as far as I can see. Fitting is dry.

-Nathan

 

[ngmtl]

On further thought, I think the slow draining could be a positive pressure issue, which would also prevent the AAVs from opening...

 

[ngmtl]

Trying to convince the building to check the whole stack because unit below us has slow draining as well and we get positive pressure and water back up from our tie-in when the apt above us uses their water (fortunately the toilets, shower, etc. all seem to be on separate stacks but it's still of concern).

General question though. While it should be obvious from my pictures, I wanted to note that there are a few inches of vertical rise in both branches between the tie-in and the traps and haven't seen too many examples that also do this. In other words, the outlet of both traps is several inches higher than the tie-in. Does this make us particularly vulnerable to positive pressure issues?

If so, are there any suggested design changes here that are possible within our constraints (can't really modify what's in the buildings wall + general geometry constraints).