Dishwasher Siphoning water

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by rsmith99, Nov 10, 2012.

  1. rsmith99

    rsmith99 New Member

    Messages:
    109
    Location:
    Oklahoma
    I have a dishwasher with a drainline that runs into the bottom of the sink cabinet and into the garbage disposal.
    When we don't use the dishwasher for a few days it starts to stink and we notice about an inch of dirty water in the bottom.

    I recently installed a new garbage disposal and did the usual checks for leaks, which included running the dishwasher.

    A minutes after the dishwasher had stopped I looked at the dishwasher drainline and I could see bubbles and water running backward from the bottom of the loop in the drainline, back toward the dishwasher.

    The dishwasher drainline is looped about 4" higher than the disposal drain.

    What am I doing wrong?

    Thanks!
    Ron

    Attached Files:

  2. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Your DW drain is BELOW the bottom of the sink, WAY below the flood rim of the sink. Mother Nature ( gravity) will assure that water flows back into that hose. Your code may or may not require an air gap....but installing one would be good. At a minimum, the drain hose should be high-looped up against the bottom of the countertop.

    [​IMG]
    Last edited by a moderator: Nov 10, 2012
  3. rsmith99

    rsmith99 New Member

    Messages:
    109
    Location:
    Oklahoma
    But it is higher than the disposal drain line. I thought that's what mattered.
  4. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Do you never have water in that sink higher than the disposal outlet???????????????????????????????
  5. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,387
    Location:
    Yakima WA
    What was it about "high-looped up against the bottom of the counter top" didn't you understand? As already point out, some areas require an air gap be installed, while other areas permit high-looping. Gotta be one or the other.
  6. Terry

    Terry Administrator Staff Member

    Messages:
    15,316
    Location:
    Bothell, Washington
    Two weeks ago I added an air gap to Sue's dishwasher. Her dishwasher drain looked just like yours. By the time she was running the dishwasher, there was so much gray water in there from the kitchen sink it was almost pouring out the door.

    It's a simple fix, and your wife will think you're a God.
  7. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,062
    Location:
    Cave Creek, Arizona
    It has to loop above the connection to the disposer, NOT the drain line. Ideally, it should loop up to the bottom of the countertop, but even that will NOT prevent siphonage, if the water in the sink is above the dishwasher's connection to the disposer.
  8. rsmith99

    rsmith99 New Member

    Messages:
    109
    Location:
    Oklahoma
    Ok. It's up against the bottom of the countertop. Couldn't go any higher without drilling a hole in the countertop.
    I understand a high loop! When I watched it siphon water, the sink, disposal, and dishwasher were empty. It was pulling water back out of the dishwasher drain line that didn't quite make it to the garbage disposal. Now all the drain line is above the disposal outlet.

    Thanks for the friendly help!
  9. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,274
    Location:
    New England
    There's a reason why all commercial dishwashers and many locales require an air gap on residential units...to specifically stop what you were seeing. Also, keep in mind that the disposer acts somewhat like a pump when you do run it, stuff drains to the area with the least restrictions. Second rule, gravity always wins!

    The instructions on ALL dishwashers say to high loop as high as possible unless you're using an air gap. They do that for a reason.
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