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Thread: Dishwasher plumbing - when far distance from sink

  1. #1
    Homeowner geniescience's Avatar
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    Nov 2005
    humid summers hot, humid winters cold

    Default Dishwasher plumbing - when far distance from sink

    I'm working on plans for a kitchen with the dishwasher located far from the kitchen sink. The drain would be about ten feet long.

    As far as I see it, the high loop has to be near the dishwasher.
    There is no countertop air gap by plumbing code here.
    After the high loop the drain line can run to the dishwasher connector Wye above the sink trap.

    An alternative to the high loop is to make a standpipe; this has the same advantage as an air gap, I believe. Probably better, as it can be higher than the counter.

    First Question
    --- Is there a maximum distance for the DW drain line ? I don't know where to find the answer.

    Second Question
    I have often seen a length of DW drain line positioned lower down than the dishwasher Wye -- the water has to go uphill to get into the Wye. I have often wondered about the standing water in it. In one of the threads here I once saw a DW line going under the floor and then coming back up through the floor to get into the sink trap. It worked. Was that because the DW machine was an old clunker with a powerful pump?
    --- So, if I have to run a length of drain line positioned _lower_ than the Dishwasher Wye, what are consequences?

    Last edited by geniescience; 08-06-2008 at 11:55 AM. Reason: spelling

  2. #2
    Master Plumber Dunbar Plumbing's Avatar
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    Apr 2005
    Northern Kentucky/Greater Cincinnati Area


    The longer that discharge hose, the greater chance for reversal of flow given the diameter of the piping.

    I've always extended those in special circumstances by using 1/2" copper tubing and heater hose found at auto supply houses due to the temperature of the wastewater when cycling.

    I've seen dishwasher 12' away from the sink. Certainly not code but you need to ask your local plumbing inspector's office. Have no clue where you live cause your location is a phrase, not an actual geographical spot.

    Why do I sound like hj all a sudden
    Read what the end of this sentence means.

  3. #3
    Retired Defense Industry Engineer jadnashua's Avatar
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    Sep 2004
    New England


    Mine runs probably about 10' to the sink. PVC with a hose barb attachment at each end for the DW hose and another piece at the sink end. The rest of the run could have been hose, but it was below the floor with a finished ceiling in the basement, and hose burried in there didn't seem like a good thing. It'd be a pain or next to impossible to snake it out if it got clogged, but that's unlikey unless there was a backup at the sink. I think the DW would force it back out when run next time, though (wouldn't if it had an air gap, though).
    Last edited by jadnashua; 08-06-2008 at 12:57 PM. Reason: added more
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  4. #4
    Master Plumber nhmaster's Avatar
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    Jul 2008
    S. Maine


    Can you put in an 1 1/2 stand pipe and trap behind the dishwasher?

  5. #5
    Homeowner geniescience's Avatar
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    Nov 2005
    humid summers hot, humid winters cold


    High loop: near sink, near DW or somewhere between the two? That is the question.

    Because I have to put the hose down at floor level
    for about eight feet length and then have it come back up
    at the sink drain DW Wye.

    Many people have routed their DW hose below the floor and then
    have it come up to the sink drain (or to the disposer). An extreme case of
    the hose under the floor for a long distance is http://www.terrylove.com/forums/show...ght=loop+floor
    -- post #12 from jadnashua describes my situation. The DW is facing the sink.

    With an air gap, the only force pushing water through to the sink drain after the air gap is gravity. (right or wrong?)

    The hose being closed in a high loop, no air gets in when the hose drops below the DW Wye level
    and only rises up to hit the DW Wye at the sink
    , so the pump has continuous water
    to push along for ten or twelve feet.
    --- This doesn't seem to be a problem as I have not heard of many DW pump failures...
    it seems to me the DW pump can handle pushing against standing water in the hose...
    (is that still valid for modern DWs?)
    and on the contrary I have seen it here and there that the pump needs to push against some pressure
    so it is not good when there is no water in the drain hose.

    The counter is higher where the DW will be, so the high loop can be higher than the sink countertop
    -- then, less chance of infecting the DW with dirty drain water.

    My na´ve thinking says that it is best to place the high loop at the DW,
    - because (higher than the sink) and
    - because then water runs downhill from there.

    Which way works best?
    High loop closest to the DW or closest to the sink?
    Which works best with DW pumps?

    I cannot install a standpipe with a P trap. (Concrete floor, in a condo, only P trap available is under sink.)
    I can use 1/2" copper for the DW drain (instead of hose).
    I could have an air gap but I don't like the noise it makes.
    -- I could make one like a standpipe with its air opening in a cupboard.


  6. #6
    Plumber jimbo's Avatar
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    Aug 2004
    San Diego


    Any indirect drain, such as a standpipe or air gap arrangement, has the potential to overflow on occasion. Usually, it would be not good! to have this happen behind the dishwasher.


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