Two 1-1/2 Inch P-Traps into Double Wye?

16 years ago

I'm working out the plumbing for our new kitchen sink, which is a large double basin with garbage disposal.

I want to use 1-1/2" pipe with mostly glued joints and am thinking of running a separate p-trap for each sink, each of which would then mate up with a double wye located in the wall cavity. The bottom drain on the double wye would drain into the fixture arm, which would be about 4 ft horizontally from the existing 1-1/2" vent and 2" drain.

The top fitting on the double wye would run back into the cabinet and terminate with a clean-out cap.

If this sounds workable, should the drain from the double wye and fixture arm be 1-1/2" or would 2" be required due to the distance from the vent.

Thanks.

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Comments (7)

lazypup
16 years ago
Your screen name is Tom in Seattle so I am assuming you are in Seattle. If that is correct, then it stands that you are the Washington State Plumbing code which is based upon the Uniform Plumbing Code (UPC).

The UPC prohibits connecting two traps to a single waste arm.

"Only one trap permitted on an arm" UPC-1001.1
Tom Pultz
Original Author
16 years ago
Thank you very much. The reason I was going to try two traps is the discharge tube that came with the disposal does an immediate 90 deg and discharges downward... which makes it very difficult to connect to the sink drain with enough height to fit the trap. I guess I should buy a straight discharge tube and then I think I can mate it up with the main sink drain using a sanitary tee, if that would be appropriate.

I'm trying to improve upon are current design, which clogs frequently. We have the standard white thread-together "sink plumbing" and the disposal discharges horizontally and connects to the sink drain with a 90 deg fitting that has a separation plate in the middle. This is very restrictive. I would like to do it all in black ABS 1-1/2" piping with suitable couplers here and there so it can be disassembled.

Regards,

Tom
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Advising others is iffy, in an internet forum. Perhaps the precise term needed goes missing, or a key concept is missed. There comes a point when it is better not to play plumber. I know enough to be aware of the limits of my knowledge for my own use. In a public forum I'll advance cautiously. Here we go. johnliu you are in California. For future reference 2007 California UPC is here http://bulk.resource.org/bsc.ca.gov/title24_part05.pdf It was manhatten42 who led me to it. There is nothing in there about a Group as large as the one you just described. Either your AHJ will consider it all still part of the Group, or not... My bet is yes, it's going to be do-able as a Group, for the reasons described in the other thread linked to in the OP about Groups. It can be done with one P trap. It can be done with two P traps. If you have two P traps or want two P traps, the connection point fitting to use is very very particular. It's described in these recent threads. http://www.terrylove.com/forums/showthread.php?36810-double-sanitary-tee http://www.terrylove.com/forums/showthread.php?36767-Single-to-Double-Sink-Vanity-%28again%29 e.g. Double fixture cross, "back to back fixture fitting", e.g. (R&G Sloane #91491 in ABS) In the second thread it is explained why not to add a wye horizontally and then connect each sink (with its own P-trap) to the two ends of the wye fitting. If connected that way, then if a draining sink got stoppered, the water draining already in the DWV pipes would siphon the other sink's P trap out, break the seal and allow sewer gases into the house. I hope that explanation meets the post-posting pick-apart scrutiny test. If your Wye you wrote about was intended to go vertically, it's also a no-go. A Wye would make the trap arm do downhill at 45 degrees, and that is a 3/4 S-trap (a no go). The reason is that you want to ensure your trap arm always remains in the horizontal plane (with a minor slope) until it reaches the vented DWV pipe. Remaining horizontal allows the trap arm to self-vent. So, no to the Wye connection. An exception is with Venting between the Trap and the Wye, but nobody ever vents first and then "Wye-combines" as it's not efficient use of wall cavity space. In some situations it is a solution to add an AAV to vent the DWV of a kitchen P trap. Learn more and hire a plumber if you need two P traps connected in new plumbing. And take no action based on learning anything from any smart person on the internet. Plumbing requires thousands of hours of training and shaping the geometry of new drains is one of the hardest subjects. hth
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lazypup
16 years ago
No matter how you hook it up the baffled tee is a code requirement when you have a disposal.

"Directional fitting required for continuous waste from a disposer or dishwasher" UPC-405.4 & IRC 2707.1
Tom Pultz
Original Author
16 years ago
OK, sounds like I'm stuck with the same, lame setup, however I think I could switch it so the disposal discharges vertically into the top of the directional fitting instead of coming in horizontally from the side... the sink drain would then come in from the side of the directional tee.

Would this be better (tend to clog less), worse, or no different?

Another thing I'm still concerned about is the current height of the fixture arm, which is at the same height of the disposal dicsharge... around 19" above the unfinished floor.

Thanks for the comments, they are very helpful.

Tom
perel
15 years ago
Sounds like you need to open up the wall and lower the tee. It's a pretty easy job. Once you have the fixture arm lower, it should be much easier to hook up correctly.

Your proposed setup would be fine under the IRC but unfortunately it's not acceptable under the UPC. Instead, you can put a vertical double wye BEFORE the trap. That way it is providing the directional fitting as required without the highly restrictive baffle tee.
lazypup
15 years ago
The problem you are encountering is a very common problem and their is a very easy solution.

Begin by removing the formed 1/4bend (90deg elbow) that came with the disposal and use a "Disposal Type End Waste Kit".

In a Disposal type end or center waste kit the cross tube to the disposal has a straight flange end that will connect directly to the disposal discharge port and run horizontal at the same level as the discharge port.

That should give you the necessary 2" clearance you need.

You can get the "Disposal Type End or Center waste kits' at any hardware or home supply in the same section as the conventional type kits.
tim45z10
15 years ago
If you have frequent clogs. You need to evalute the remaining discharge line and what you are putting in there to begin with. Put food preparation scraps into the compost or trash.

Two 1-1/2 Inch P-Traps into Double Wye?

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lazypup

Tom Pultz
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Two 1-1/2 Inch P-Traps into Double Wye?

Comments (7)

lazypup

Tom PultzOriginal Author

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lazypup

Tom PultzOriginal Author

perel

lazypup

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Tom Pultz
Original Author

Tom Pultz
Original Author