Connect Two New Sinks To Drain Line for Original Sink?

13 years ago

I have a double-bowl kitchen sink that lives under a pair of windows. The windows are separated by a 5'' molding. I am not sure if the drain is vented via a line up through the wall behind the molding, or if the vent line goes to the side of the window pair, where a plumbing stack lives (the drain for the second-floor bathroom toilet lives there, I'm not sure what else) There is no AAV in sight.

I plan to change this to two single sinks, about 34'' apart, flanking the location of the original sink and the original drain line and supply lines. Both sinks will have disposals.

Is it acceptable to plumb both single sinks to the original drain line using slightly sloped runs to a wye at the original drain line? And to supply both faucets from the original supply valves in the wall, using tees? Or, is it better practice (or required) to open the wall and run new, separate drain, vent, and supply lines?

The house is conventional wood-frame construction with an unfinished basement so there is good underside access for the re-plumbing. But running new vent lines would be a pain. I'd like to minimize cost if I can. I live in Portland OR.

Thanks for any thoughts.

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Comments (3)

John Liu
Original Author
13 years ago
Oh, more info if it helps. Oregon uses the UPC as far as I know. The trap arms would each be about 16'' long, if I use the existing drain. One sink would also serve to drain the dishwasher, via the dishwasher drain fitting on the disposal.
tim45z10
13 years ago
They have kits just for connecting 2 sinks to one drain line.
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davidro1
13 years ago
... supply both faucets from the original supply ?
Yes.

... plumb both single sinks to the original drain ?
You must specify how you meant it.
You have three choices:
"with separate P traps"
"on one P trap"
"whatever will be best in my view after I learn more".

Having one P trap is do-able, and the kits can be web searched using key words "Tubular Continuous Waste". The length of the horizontal part is not a problem. It's the same principle as when one connects a disposer to the one and only P trap located under the second sink drain. One Ptrap is all that is required for two drains. The "trap arm" comes after the P trap. Your trap arm you already have can be used for two sinks and a DW.

The horizontal pipe upstream to the P trap is not called the "arm" . johlliu in your 2nd post you said "The trap arms would each be about 16'' long, if I use the existing drain" . Here you may have meant the pipe in "Continuous Waste" kits.

But since you used the word "Arm", someone might come in and advise you on the scenario of two Ptraps.... Because two arms means venting each arm prior to the Wye you mentioned. Did you really mean that you wanted two P traps? (Maybe you just want to do the most possible, optimal, up to a certain point.) Do you really want to have two P traps? To know whether installing 2 Ptraps will be easy or hard, you have to talk to the local AHJ to see what their stance is on using AAV's to vent trap arms, or redoing the venting in the wall. For the discussion it would help if you knew where venting was in your wall

Everything written above may need to be redefined more precisely. I'm not a plumber, not a plumbing inspector, not a plumbing instructor, nor do I play one on any TV show or in this site or any other site.

hth