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Thread: Laundry Tub Drain Help

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  1. #1

    Default Laundry Tub Drain Help

    Hey guys,

    Need some advice. I've got a 1.5" copper drain line that come up out of the ground and has a brass 90 elbow on top that enters a p-trap that goes into the bottom of the laundry tub.

    What I'd ideally would like to do is cut the copper and put in an additional out area so I can run the washer right into it as opposed to into the laundry tub.

    Here is a drawing to illustrate.

    Will this work and if not what is the best option?

    Also what is the best way to convert from copper to PVC if the plumbing has to float in mid air?


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  2. #2
    DIY Junior Member acjensen's Avatar
    Join Date
    Aug 2007
    St. Cloud, MN


    sounds like you have an s trap for your laundry room sink, which has no vent, and are not allowed by code in most if not all areas.
    can you run a vent up thru a wall into your attic to tie in with an existing vent, or to run it out your roof? an AAV (air admittance valve) may be ok, but I don't know anything about those, someone else should have more info on if that's a good option for you.

  3. #3
    Forum Admin, Expert Plumber Terry's Avatar
    Join Date
    Aug 2004
    Bothell, Washington
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    Something like this would work.

    If you have a 2" fitting that the 1.5" is going into, remove the 1.5" and start with 2"
    Newer code calls for 2" on a washer drain.

  4. #4
    Engineer Furd's Avatar
    Join Date
    Jul 2007
    Wet side of Washington State


    If your drain is only 1-1/2 inch then I strongly suggest that you continue to dump the washing machine into the laundry tub. Most washing machines built in the last several years have drain pumps that will overload a 1-1/2 drain and if you try to make a direct connection (without the intervening laundry tub) you will end up with the drain water overflowing the standpipe and gushing all over the floor.

  5. #5



    That is almost the exact scenario that I have. My entire house lacks proper venting. Slab home built in the 50's.

    Based on Furd's point I'm going to leave it as is and continue dumping into the laundry tub. Oh well.

    Thanks for the tip guys.


  6. #6


    Agree on prior suggestions to get a vent in there and use 2" where possible.

    Having said this, you will not always have a wet floor if using a 1.5" pipe. This is a common alarm spoken by many forums.
    There are many, many situations out there where 1.5" pipes work, albeit not current code, but sometimes you can't (or don't need to) bring it in line with new code.

    Most full size washers need 17 gal/min carry-away capacity. Small stackables, and new energy efficient model use much less water and don't necessarly evacuate at the same high rate (more like 12 gal/min). You need to look at your situation. For example, using 1.5 ID pipe and having 10' in length horizontal and 36" of standpipe will move 21.25 gal/min. Granted, a 2.0 ID pipe will allow a water discharge of 37.78 gal/min under the same configuration. Both will move the 17 gal/min needed by a full-size washer. Keep in mind that Lint is your enemy when it comes to the washer and a 1.5" pipe will develop an unrecoverable situation prior to the 2" pipe.

    The height of your standpipe plays an important factor as well. A pump designed to move 12 gal/min @ 3 feet will likely move something like 7 gal/min @ 8 feet. I'm not saying that it is reasonable (or code) to have an 8' standpipe but just another reason why it is not that easy to say, 'you'll have a wet floor'.

    Just my 0.02


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