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Old 08-13-2016, 04:46 AM   #1
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Draining laundry sink into washer stack with trap in slab


I would like to add a utility sink next to washer but all I have to work with is the washing machine open drain pipe that sticks up out of the slab. The trap is under the slab AND the vent stack is in another room so it cannot be tapped into. After reading some posts it doesn't sound like there is a way to do this to code so I'm just hoping for recommendations on best hack.

Right now I'm leaning towards just adding a wye to the standing washing machine pipe about 14" up and have the sink drain directly in there without even using a ptrap on sink. Is the worse that can happen is the washer could drain too fast and push water into the sink?

Is there a best way to do this by adding a AAV or something even if it is not up to code?

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Old 08-13-2016, 12:14 PM   #2
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Re: Draining laundry sink into washer stack with trap in slab


I am not a plumber but i do plumbing work on my rental properties. I would suggest getting a PVC wye with a 1 1/2" inlet for the laundry tub drain and the other ends of the wye sized to fit the standpipe. I would also get a 1 1/2" P-trap and tailpiece for under the laundry tub. At the wye you will also need a street trap adapter (street simply means that the trap adapter glues directly into the 1 1/2" arm of the wye). Cut the existing standpipe at a height that will give you 1/4" fall per foot of run.

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Old 08-13-2016, 01:29 PM   #3
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Re: Draining laundry sink into washer stack with trap in slab


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I am not a plumber but i do plumbing work on my rental properties. I would suggest getting a PVC wye with a 1 1/2" inlet for the laundry tub drain and the other ends of the wye sized to fit the standpipe. I would also get a 1 1/2" P-trap and tailpiece for under the laundry tub. At the wye you will also need a street trap adapter (street simply means that the trap adapter glues directly into the 1 1/2" arm of the wye). Cut the existing standpipe at a height that will give you 1/4" fall per foot of run.

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Will not fly. Install the slop sink using the existing drain. Drain the washer into the sink.
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Old 08-13-2016, 01:33 PM   #4
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Re: Draining laundry sink into washer stack with trap in slab


Can you explain why you state that my suggestion will not fly? Just trying to educate myself.

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Old 08-13-2016, 01:39 PM   #5
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Re: Draining laundry sink into washer stack with trap in slab


You are overloading the 1.5" drain. Some new washers by themselves will flood a 1.5" drain. New code requires 2" for washers.
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Old 08-13-2016, 01:43 PM   #6
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Re: Draining laundry sink into washer stack with trap in slab


Not sure I understand. In my suggestion, the washer would remain connected to the standpipe. Are you saying that because the sink could be draining at the same time as the washer that it could flood?

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Old 08-13-2016, 02:22 PM   #7
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Re: Draining laundry sink into washer stack with trap in slab


I see no problem with taping into the washer stand pipe with a 1 1/2 sanitary tee.
Since the trap is below the floor a trap for the sink should not be necessary.

Granted some codes row specify a 2" for a washer stand pipe that is for new construction. It is also contrary to logic because the present rage in clothes washers is low water usage.

Just do it, it will work. If anything the washer would back up into the sink temporarily. Since you indicated the stand pipe is properly vented no need for an AAV.

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Old 08-13-2016, 02:41 PM   #8
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Re: Draining laundry sink into washer stack with trap in slab


New washers are low water usage but the pump the waterr out very fast.
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Old 08-13-2016, 02:45 PM   #9
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Re: Draining laundry sink into washer stack with trap in slab


Again, i am not a plumber but i dont understand something. If you dump the washer outflow into the laundry tub, that laundry tub will have a 1 1/2" outlet. Do they now make laundry tubs with a 2" outlet? If so, i have never seen one.

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Old 08-13-2016, 02:51 PM   #10
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Re: Draining laundry sink into washer stack with trap in slab


No slop sinks have 1.5" drains. The difference is the sink acts as a buffer. It holds the washer outflow long enough to let it drain.
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Old 08-13-2016, 05:12 PM   #11
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Re: Draining laundry sink into washer stack with trap in slab


This forum is great. I am planning to go with Jeff's recommendations. The existing pipe is 2" so hopefully I can just add a 2" wye with the 1 1/2" inlet for the sink. The sink will rarely be used so this approach seems cleaner than draining the washer into the sink. It is a LG high efficiency front loading machine with a very small drain line which I assume means it doesn't drain lots of water unless it is at a higher pressure.
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Old 08-13-2016, 10:38 PM   #12
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Re: Draining laundry sink into washer stack with trap in slab


Quote:
Originally Posted by pkcinna View Post
I would like to add a utility sink next to washer but all I have to work with is the washing machine open drain pipe that sticks up out of the slab. The trap is under the slab AND the vent stack is in another room so it cannot be tapped into. After reading some posts it doesn't sound like there is a way to do this to code so I'm just hoping for recommendations on best hack.

Right now I'm leaning towards just adding a wye to the standing washing machine pipe about 14" up and have the sink drain directly in there without even using a ptrap on sink. Is the worse that can happen is the washer could drain too fast and push water into the sink?

Is there a best way to do this by adding a AAV or something even if it is not up to code?
Yes there is, either use the standpipe for the sink tailpiece and drain the washer into the sink- or, if the vent is 2" cut a tee into it and run a new trap arm to the sink. This is called a horizontal wet vent.

It is not code to have 2 fixtures on one trap (there are exceptions and this isn't one)
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Old 08-13-2016, 11:43 PM   #13
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Re: Draining laundry sink into washer stack with trap in slab


Seems like the general concensus is adding a wye into the 2" existing pipe will work fine. Even though it is not up to code I'm going to give it a try. Having the washer drain into the sink just sounds like more problems since someone could plug the sink and fill it with water and then if a load of laundry is run it would over flow the sink... or if someone put something in the sink expecting it to stay dry the washer would get it wet.
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Old 08-14-2016, 08:06 AM   #14
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Re: Draining laundry sink into washer stack with trap in slab


If you are going to take that route, i would still strongly suggest that you install a P-trap under the sink.

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Old 08-14-2016, 09:50 AM   #15
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Re: Draining laundry sink into washer stack with trap in slab


Right. I already have the p-trap installed since it came with the sink kit. I'm a plumbing novice and my first impression was a p-trap is not needed since I read it is used to prevent gases from coming out the drain and this case the laundry room open vent stack already lets air into the room.

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