Ask Me Help Desk - Double sink trouble

Hello all,
I recently changed our bathroom sink from a single bowl to a double and I am starting to have troubles. When I run the water on one side the other sink fills up, when I turn off the water it does drain though. I talked to "a guy" at Lowe's originally when I installed it and he said that I wouldn't need a trap. My question is: DO I need to put a trap in and if so do I need to put one on each side? I tried Drano to no effect and took apart the pipes and couldn't find a clog. The sinks drain into one line at the wall. Im thinking that I need a trap(s) but just not sure. If traps are necessary do they need to hang lower than the outlet pipe? Thanks for any help you can provide, I did do a brief search on this forum for this question but couldn't find anything.

Thanks again

Matt

Quote:

Originally Posted by MGamble

Hello all,
I recently changed our bathroom sink from a single bowl to a double and I am starting to have troubles. When I run the water on one side the other sink fills up, when I turn off the water it does drain though. I talked to "a guy" at Lowes originally when I installed it and he said that I wouldnt need a trap. My question is: DO I need to put a trap in and if so do I need to put one on each side? I tried Drano to no effect and took apart the pipes and couldnt find a clog. The sinks drain into one line at the wall. Im thinking that I need a trap(s) but just not sure. If traps are necessary do they need to hang lower than the outlet pipe? Thanks for any help you can provide, I did do a brief search on this forum for this question but couldn't find anything.

Thanks again

Matt

Matt you absolutely need a trap under your sink. I personally prefer and would recommend to trap both sinks directly under each sink drain. Some people will trap first thing out of the wall and then use a T piece that then connects to both sinks. You have less of a chance of getting a smell back in your line if you trap under both sinks directly.

If you have a piece of pipe coming out of the wall that you can convert to PVC and easily get on to, I would recommend using a PVC twin drainage L which would allow you to go both directions with PVC pipe and trap on both sides. Good luck.

[QUOTE=MGamble]Hello all,
I recently changed our bathroom sink from a single bowl to a double and I am starting to have troubles. When I run the water on one side the other sink fills up, when I turn off the water it does drain though.

Pictures of the current set-up would be really helpful at this point.

I'm not exactly sure what a "PVC twin drainage L" is, but it doesn't sound like anything a reputable Plumber would install.

The picture below is the correct configuration for draining two lavatories.

Obviously, if you are in the pre dry wall stage your set up is optimal. A 2" cross with two horizontal branch drains terminating under each sink is best. In the situation where you have finished drywall and cabinets in place and only one drain outlet, your solution simply wouldn't be feasible without much unnecessary work by the homeowner.

As for the PVC Twin L, I'll include a picture from Charlotte's website. It's as legal as a single 90 would be on a lavatory drain. A Wye or double combination would also be acceptable, but the combination would add another leak potential because of the cleanout adapter out of the back that would have to be installed.

This reputable plumber finds no problem with this solution to the individuals situation, unless the plumbing code has suddenly restricted the use of elbows.

http://i104.photobucket.com/albums/m...hael/twinl.jpg

Quote:

Originally Posted by malex27

Obviously, if you are in the pre dry wall stage your set up is optimal. A 2" cross with two horizontal branch drains terminating under each sink is best. In the situation where you have finished drywall and cabinets in place and only one drain outlet, your solution simply wouldn't be feasible without much unnecessary work by the homeowner.

Being a stickler for 'by the book' Plumbing, I have to ask myself why he didn't pull the cabinet base and have it roughed in correctly when he was replacing or modifying the original countertop -- The photo below is just such a scenario, the homeowners wanted to add lavatory, so I walked them through the procedure for doing so and since the drywall was cut well below the countertop height, it was a simple matter of installing a piece of drywall and then taping and mudding the joint.

Quote:

As for the PVC Twin L, I'll include a picture from Charlotte's website. It's as legal as a single 90 would be on a lavatory drain. A Wye or double combination would also be acceptable, but the combination would add another leak potential because of the cleanout adapter out of the back that would have to be installed.

I figured that was the fitting you described -- Under the UPC, it is listed as one of a number of 'Prohibited Fittings'.

Particularly if used as a horizontal/horizontal transition.

But hey, the UPC is the governing code in only about 10% of the country.

Quote:

This reputable plumber finds no problem with this solution to the individuals situation, unless the plumbing code has suddenly restricted the use of elbows.

Yeah, I cringed a bit when I reread that this morning -- Sorry about that.

Well, don't take it too personally, Speedball and Doug and I have diasagreed a few times ourselves over issues directly related to the different expectations of our differing codes.

Thanks for all the help. I wish I was a plumber so I would know what to do. In my situation though I'm not exactly going to be able to follow the pictures posted above. I only have one wall outlet for the water to flow out. So I plan on putting a trap under each sink and then have that flow out. If that's not going to work, I guess I'll have some sheetrock questions for you all later then ;)

You could try installing a continuous waste, as Speedball suggested in a similar discussion, minus the branch for the dishwasher, of course.

Quote:

Originally Posted by MGamble

Hello all,
I recently changed our bathroom sink from a single bowl to a double and I am starting to have troubles. When I run the water on one side the other sink fills up, when I turn off the water it does drain though. I talked to "a guy" at Lowes originally when I installed it and he said that I wouldnt need a trap. My question is: DO I need to put a trap in and if so do I need to put one on each side? I tried Drano to no effect and took apart the pipes and couldnt find a clog. The sinks drain into one line at the wall. Im thinking that I need a trap(s) but just not sure. If traps are necessary do they need to hang lower than the outlet pipe? Thanks for any help you can provide, I did do a brief search on this forum for this question but couldn't find anything.

Thanks again

Matt

Matt,

This boils down to a simple choice. Come out of the wall with a wye, ( sorry Malex but your double ell won't fly) and install a single trap for each lavatory or you and install a trap on the nearest lav and use a continuous waste,(see image) to tie lav #2 back to the trap. As Growler has pointed out a regular tail piece's used instead of the branch tailpiece shown. This method has benn used on both kitchen sinks and twin lavatories with no back up problems.
Good luck, Tom

Speedball that's your opinion and your welcome to it friend. Saying it "simply won't fly" is nothing more than an opinion that isn't based on the IPC in any fashion. A wye will work but it will also take up 3 or 4 more inches of front to back cabinet space.

Nothing more than a difference of opinion and technique.