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Thread: Looking for advice on tying in washer to septic drain

  1. #1
    DIY Junior Member cxoffers's Avatar
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    Default Looking for advice on tying in washer to septic drain

    Hello from Vermont, Been reading forums for a while and thought I'd finally ask a question.

    I'm going to connect a new washer to the existing main line this weekend. I think I have it figured out but would like opinions.

    The main drain line in basement runs at 7ft. high the length of house to south facing wall. About 12" from wall it takes a 90* bend, drops 4.5' then takes another 90* bend and exits south wall to septic.

    I'm installing washer about 5' to the right of where drain pipe drops and exits wall. Back of washer will be against south wall.

    My plan is to cut into vertical part of drain pipe and install a sanitary-T then a 2" P-trap going towards washer, then install two 90* bends to bring drain line closer to wall, 2nd 90* will be slightly pointing upwards so I can install a 2" drain line rising 1/4" per ft. until it's close enough so washer drain can be put into it.

    Questions are: How high should a cut into main 3" main drain? Is a sanitary-t the proper choice and should the end point where drain meets washer drain tube be vertical?

    Thank you and thanks for a great resource for us DIY'ers!

  2. #2
    Moderator & Master Plumber hj's Avatar
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    1. The cut in should be as low as possible
    2. The "P" trap should be at the washing machine, NOT at the connection to the drain line
    3. The trap should have a vent, and an AAV is NOT a good alternate when it is in the basement
    4. IF the septic tank backs up, ALL the sewage will overflow out of that washer drain. It might be particularly catastrophic if the backup is due to a flooded drain field and your washer drain is trying to drain the whole acre.
    Licensed residential and commercial plumber

  3. #3
    DIY scratch-pad engineer leejosepho's Avatar
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    RE: advice on tying in washer to septic drain

    If that line goes out to an actual septic tank and a drainfield system of whatever kind, you should take a close, analytical look at all of that existing system before adding the output of a washing machine. At the last home I owned, the septic system would have never held up with a washing machine's output added, and I had to do a lot of improvement (a separate drainfield, in my own case) to get rid of the washing machine being discharged onto the ground like it was when I first got there.
    "Great minds discuss ideas, average minds discuss events and small minds discuss people." --Eleanor Roosevelt

  4. #4
    DIY Junior Member cxoffers's Avatar
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    Thanks for replies- Having the p-trap at washer ends makes sense although some of the books I have and photos online show it on the opposite end? Not really sure what an AAV is? Not worried about added capacity of washer to septic. We're just moving the washer to a new location and it's been hooked up to septic for life of house.
    Only question is, if I cut in low in 3" mainline I'll need to angle 2" line up until I level off and install p-trap. Should I use a Y since angle is already in it or a sanitary t with some 45* angles added.

  5. #5
    DIY Senior Member Chad Schloss's Avatar
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    I owned a home with a setup like yours. the p trap was high on the wall and dumped right into the main drain exiting the foundation. worked fine for the 5 years i was in there, and the 5 years before that i assume. i had to get an extention hose for the washing machine drain. once in awhile some of the water remained in the tub. a one way check valve placed in the line at the lowest point possible would help.

    If the septic does get too backed up, water can and will come out of the standpipe for the washing machine, since it is the lowest point on the system. never happened with our place, had the tank pumped regularly.
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  6. #6
    Moderator & Master Plumber hj's Avatar
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    Go horizontal to the "P" trap and use a longer riser. Using ANY KIND of "angle" will just make the lack of a vent worse.
    Licensed residential and commercial plumber

  7. #7
    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by cxoffers View Post
    Having the p-trap at washer ends makes sense although some of the books I have and photos online show it on the opposite end? Not really sure what an AAV is?
    AAV = Automatic Air Vent (like sticking up from a Tee in the line needing vented)

    The deal with the trap location is to not have what is known as a "running trap" at the end of a line. I once did that while using 2" PVC for a long run from a tub and did not have any trouble, but Code does not allow that even though it can work just fine.

    When I once had a washing machine located like in Chad's picture, I sat a lidded drum next to it for the washer drain and then used a pedestal pump to push the grey water up to the line going out at the top of the basement wall. By doing that, the washer could pump itself out completely and the sump's check valve kept anything from coming back into the basement.
    Last edited by leejosepho; 08-20-2012 at 06:58 AM.
    "Great minds discuss ideas, average minds discuss events and small minds discuss people." --Eleanor Roosevelt

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