New Dual Vanity Draining Slowly And Backing Up

[Seth B Rosenberger]

Hi, I am hoping for some advice to help me fix my issue and more importantly, understand what I did wrong.

I have a new dual vanity that I decided to plumb with two traps. I thought it would be better than one but obviously with my setup, I was mistaken. If I run either sink alone, they work flawlessly. If I run both together, after a few seconds they start draining slowly and backing up. What went wrong and is my setup salvageable or should I just use one outlet and tie them together under the vanity itself while plugging the other outlet.

Please see attached pictures for my setup. I did this a few months ago so I'm 99 percent sure I am set up like the first picture but there is a small chance it is like the second.

https://photos.app.goo.gl/TtUcVTv1biFDCJ9NA

https://photos.app.goo.gl/HgJPMBeGAGY3Gbtq5

As a final note, I tried adding AAVs just to see if that solved my problem. I thought maybe I had created negative pressure that could be relieved. They did not solve the issue but obviously, I couldn't get them above the flood rim since I just threw them under the vanity itself as a test.

Thanks in advance

 

[hj]

What is the difference between the two photos? It is not how I would have done it, but it should NOT affect the draining whether one or both sinks are being used.

 

[Sponsor]

 

[Seth B Rosenberger]

What is the difference between the two photos? It is not how I would have done it, but it should NOT affect the draining whether one or both sinks are being used.

In one, the first outlet is directly above the stack and in the other it is slightly offset towards the second outlet.

These faucets have a very high flow that I needed to turn down at the valve. Could that cause an issue of too much flow that then in turn creates a venting problem?

The faucets are fed by one shared 1/2 copper line at around 65 to 70 psi so I didn't think that could be the issue.

Could the increased flow have uncovered a pre-existing vent blockage that can't keep up with the higher flow?

Thanks

 

[Seth B Rosenberger]

Hi guys, any suggestions or ideas here? I'm really at a loss.

I also confirmed that the setup is as shown in the first picture.

Thanks

 

[Reach4]

You should have added a cleanout for the vertical drain pipe. The problem is not venting.

If you put a trap adapter at the wall, that could be used as a cleanout. Not as good as a cleanout would have been, but get that drain rodded going down. There is a good chance that the slowdown is where that drain line then switches to horizontal below the floor level.

 

[WorthFlorida]

What are referring to as "outlets"? Does each sink have its own trap and connection to the drain pipe leading to the stack? Poor venting generally has bubble or gurgling sounds. How about a picture of the trap setup for both sinks. Any pictures when the wall was opened up to add the second drain. In the wall does the drain pipe turn down 90 degrees or does it make a 90 degree turn to the left ot right and run horizontal with slope to the stack?

What type of material is your drain pipe and what size pipe is in the wall including size of the vent pipe? It all should be 2" to the three or four inch stack and with traps at 1-1/4" for bathroom sinks. Do you know the approximate distance from the traps t0 the main stack? If you're in an old building with cast iron and galvanized steel pipe, the pipe to the main stack is probably has some blockage or too small for two sinks at once. Anything smaller than 2" will have issues. It does drain, no odors and an AAV proved you don't have a vent problem, you may have to live with it. Don't waste your money buying Drano, it would work.

 

[Reach4]

This is what he reports the piping to be, from his first picture:

I wonder what the actual fittings are.

 

[Seth B Rosenberger]

Yeah, thanks for reposting that Reach4. Fittings are sanitary tees. And a short sweep 90 degree for vent above the second stub out. I do have a trap adapter and should be able to clean it out fairly easily from up here or from downstairs. The main stack is 1.5" cast iron connected up to pvc behind the vanities with a shielded coupling.

I actually think I found my problem. I connected both sinks to one trap and had a small leak from a compression fitting. When I went to remove the trap to adjust a bit I had lots of water pour out.

I remembered back to the fact that my guys had to open this wall up again for non plumbing related issues and I think somebody must have removed my supports for the pvc pipe and never put them back. Now, the stub out on the right is half an inch LOWER than the one on the left. ‍♂️ I assume that is something that could be causing an issue like this? Btw, I don't know why I wrote 28 inches between vanities since it is actually 24.

Assuming this is the issue, any ideas on a remedy that doesn't involve breaking open the wall? I can probably support stub out #2 from under the vanity, cap it off and just keep the 1 trap setup. Is there anything there against code? If I can't support it well and I keep the one trap setup, is there anything against code or potentially hazardous with a capped stubbed out that is lower than the one trap that remains in use?

Thanks all for the questions and advice.

Thanks all

 

[Seth B Rosenberger]

And Reach4, looks like you were absolutely correct that this is an issue with my drain and not my vent.

I guess I was just noticing it with both sinks in because of the increased flow.

I have been going crazy for something that should have been so obvious.

 

[hj]

WHY do you keep referring to the "one trap connection. when you have TWO openings in the wall?