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Thread: Sink and dishwasher drain to abandoned washer standpipe

  1. #1
    DIY Junior Member pnbrownsr's Avatar
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    Default Sink and dishwasher drain to abandoned washer standpipe

    Hello, I have been viewing this forum for several years and have gotten some excellent advice here, and have as a direct result of this forum replaced all my toilets with Toto Drake toilets. The advice here is outstanding.

    My daughter and her husband recently bought a home in central Florida near us which was built in 1955 and is all on a slab with a septic system. There is an interior wall of her kitchen where there used to be a desk and washing machine. She would like to install a sink and dishwasher on that wall. (Please note that we DO NOT want to drain a washing machine there.) We were thinking of draining the sink into the old washer standpipe which is 1 1/2" ID galvanized with no visible trap. I pushed a hand operated snake as far as I could down the pipe and it bottomed out at about 18" or so below the top of the slab. I poured water down the standpipe and heard a little gurgle so I am thinking there is a trap under the slab. Hidden in the wall behind and just to the left of the standpipe is a vent stack, and nothing else is venting on that stack.

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    Somewhere on the site I read that you can not have 2 traps in series, and if that is the case then I guess we could not use the standpipe to drain the sink and DW, and I do not like the idea of no access to the trap if the standpipe is permitted to be the drain. The sink would be just to the right of the standpipe, so I think we can meet the trap arm distance. requirements. I can give better measurements if that would help

    The other option we were thinking of is tying into the vent stack, if that would be permissible. How do I best verify that the vent stack does indeed go all the way down thru the slab to the main drain to the septic?

    All advice will be much appreciated.

    Pat

  2. #2
    DIY Senior Member asktom's Avatar
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    There is no simple way that is right. The existing WM drain should be 2" drain and the trap should be above the floor, so there are problems going into this. You don't want to put another trap and dump into the standpipe, that will only cause problems and be way wrong. You could dump the sink (w/ the DW connected via a branch tailpiece) into the standpipe, but that would create a tailpiece dropping down farther than code (at least the UPC) allows and would tend toward causing the trap to syphon, a bad thing. The other option is to bust the wall and tie into the vent, but it is probably 1 1/2" and code requires 2" - it is hard to imagine it was run with a 2" vent and a 1 1/2" standpipe. The right way is to find 2" under the floor and re-run the works, tying into the existing vent. I suspect that is not going to happen. Others may disagree, but if the floor isn't going to be nuked, I would lean toward tying into the vent (undersized though it is) and capping the existing standpipe. My thinking is that while the the drain may be prone to backing up, that is better than syphoning the trap.

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    DIY Senior Member jim mills's Avatar
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    Too many assumptions to give advice. Verify what you have, then we can go from there.

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    DIY Junior Member pnbrownsr's Avatar
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    Thanks very much for the replies. Tomorrow I will measure the vent stack and report that. I am tending toward Asktom's recommendation of opening the wall and tying into the stack, especially if it turns out to be 2"

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    Test, Don't Guess! cacher_chick's Avatar
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    There should never be a drain of less than 2" below grade, so the only right thing to do is verify what you have and make your new install in accordance with the appropriate plumbing code.

  6. #6
    DIY Junior Member pnbrownsr's Avatar
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    I have confirmed that the vent is 2" cast iron so we will tie into the vent (with the Fernco type shielded couplings) and cap off the old washer standpipe as suggested by Asktom. We really do not want to go into the slab for this install.

    Thanks to all for their helpful comments.

    Pat

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