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  1. #1
    Join Date
    Oct 2011
    Posts
    1

    Default Does dishwasher need an arc in the drain?

    Step 7 of How to Install a Dishwasher says,"Hold the hose and strapping against the back of the cabinet so it makes an arc that's higher than the drain inlet." Can you tell me why? I want to run the drain hose down thru the floor without the "arc" so I can winterize (drain) the system. That "arc" would cause me a problem during the winter months.

    Thanks for the advice everyone. I should have done a better job with my original post. The DW is a new install. It won't be next to sink. It will be on other side of room. (Tiny Kitchen) Has separate water feed and own drain to basement hookup. So not worried about back flow. I am concerned that that "arc" is necessary for the proper operation of the DW (like a clothes washer). If the elevated hose or "arc" is only to prevent back flow, and not relevant to the DW's operation, then I'll be in great shape. Thanks again all!
    Last edited by abfcpo; 10-26-2011 at 07:29 PM. Reason: Clarify original Post

  2. #2
    Join Date
    Dec 2010
    Location
    Houston Texas
    Posts
    2,969

    Default Re: Does dishwasher need an arc in the drain?

    The arc keeps the drain water from the sink from running backwards into the DW hose and realllly stinking up the place.

  3. #3
    Join Date
    Jan 2009
    Location
    Needham, MA
    Posts
    559

    Default Re: Does dishwasher need an arc in the drain?

    houston is correct, you have to create an inverted trap with the DW hose so that sink/drain/garbage disposal water doesn't run back to the DW. i've seen it many many times, as soon as a customer complains that a DW isn't working or draining properly or is smelling that's usually the culprit.

  4. #4
    Join Date
    Jul 2010
    Location
    SoCal
    Posts
    6,694

    Default Re: Does dishwasher need an arc in the drain?

    Install an air gap in the sink and you won't have any problem.

  5. #5
    Join Date
    May 2008
    Location
    Pacific Northwet
    Posts
    1,643

    Default Re: Does dishwasher need an arc in the drain?

    As others have said, the arc is necessary to prevent backflow into the dishwasher (and an air gap above the counter is even better). It's required by code.

    However, you've mentioned that you want to be able to fully drain the dishwasher to protect it from freezing, and it's nowhere near the sink. So you probably could get away with going straight down, but the inspector might not pass it if you did.

    Some dishwashers have a drain solenoid valve (not sure about all), so I would think that the water shouldn't all drain out until it's supposed to.

    If you do end up putting the loop in, when you want to winterize the dishwasher, just dump some RV antifreeze in and pump it out. The remaining antifreeze should protect the DW.

    (This whole backflow thing makes me wonder why backflow preventers aren't required on the INLET of dishwashers. I mean, isn't there a possibility that a burst pipe could suck nasty washwater back into the supply lines creating a health hazard? I believe they are required on commercial dishwashers; not sure why not on residential.)
    The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.

  6. #6
    Join Date
    May 2011
    Location
    Northern Virginia
    Posts
    99

    Default Re: Does dishwasher need an arc in the drain?

    Quote Originally Posted by abfcpo View Post
    Step 7 of How to Install a Dishwasher says,"Hold the hose and strapping against the back of the cabinet so it makes an arc that's higher than the drain inlet."
    People, I still don't know how high the arc should be.

    Normally, the DW drain hose is tapped to the kitchen basin drain (the garbage disposal is also tapped to the same drain just below the basin drain assembly). So how high the arc ? above the bottom of the kitchen basin ??

    Thanks.

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