Dishwasher drain connection

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by msehler, Nov 3, 2012.

  1. msehler

    msehler New Member

    Feb 20, 2008
    I am replacing my garbage disposal and ran into a question I can't seem to answer easily. I currently have a 50/50 split sink, one side with a disposal (which quit working and started leaking). I got a new insinkerator evolution, 3/4hp to replace the badger 5, 1/2hp. The dishwasher is currently connected to the NON-disposal side of the sink via a wye connection affixed in the horizontal before the P-trap (which I believe is up to UPC--I'm in Kansas, if that helps).
    Is it preferential to relocate the dishwasher drain to the disposal? if so do I need an air gap? Or does the disposal function as an air gap? I've read about the air gap but it seems like every other thing I see says "if no disposal you need an air gap" or "if using a disposal you need an airgap", but not the other way around (contradictory information). I do not have an airgap in my current arrangement.

  2. kreemoweet

    kreemoweet In the Trades

    Sep 7, 2009
    Seattle. WA
    The requirement for an air gap has nothing whatever to do with the presence or not of a garbage disposal. I've also not
    seen any plumbing code expressing a preference for connecting the dishwasher drain to disposal versus sink tailpiece.
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  4. Terry

    Terry Administrator Staff Member

    Aug 17, 2004
    Bothell, Washington
    The Air Gap, or High Loop is meant to keep waste water from the kitchen sink, and backed up waste water from the home from entering your dishwasher, where hopefully you will be washing and sanitizing your dishes.

    Regards of where the drain enters the system, it will need either an air gap or a high loop.
    The High Loop, is the tubing installed as high under the counter as possible. It does not guarantee that water will not back up into the dishwasher. An Air Gap does.

    You can drain the dishwasher in several ways after you have handled the Air Gap situation.

    A Wye or tee below the sink
    Punch out the disposer and drain it there
    A separate p-trap for the dishwasher
    A Johnson Tee, mostly seen in the Seattle area. It's named after a plumbing inspector here.

    Air gap into a disposer.
  5. msehler

    msehler New Member

    Feb 20, 2008
    There is a small blue plug type apparatus directly below (sewer side) where the dishwasher drain is connected. Could this be a back-flow preventer (to prevent sewer from backing into sink or dishwasher)? Is it preferred to run the dishwasher into either the disposal side or the NON-disposal side?

    I currently have what I believe to be a high loop situation (previously installed) draining into the NON-disposal side.
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    It doesn't matter which side it goes into! On a new installation that included a disposer, they'd probably use the disposer inlet designed for it as it wouldn't require extra parts. Since you have an inlet for it, if you were to use the disposer, you'd have to replace that connection. So, if you're going to do that anyway, I'd just run it to the disposer, if not, leave well-enough alone.

    An air gap is a safety device...required some places, recommended everywhere.
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