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Thread: Dishwasher drain

  1. #1

    Default Dishwasher drain

    Hello. I am getting ready to replace my ~20 year old dishwasher and took a look under the kitchen sink to find a separate drain for the dishwasher (dishwasher rubber discharge hose connected to copper pipe in Photo1). I also took a look in the crawlspace under the kitchen where these two pipes pass through the floor. There are p-traps on the sink drain and dishwasher drain underneath the floor before they connect into the main stack.

    1. Should I continue to use this separate drain line? or use the dishwasher drain connection on the garbage disposer and cap the dishwasher drain line?
    2. Is there any benefit to having a separate dishwasher drain line?

    Thanks.



    Photo1


    Photo2

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    Well, what you have is not up to code! In most places, the trap must be above the floor, plus, if you actually have a second trap below the floor for the sink, that's not up to code either. The top one is a S-trap, which is not valid, either. Where is the vent, if there is one?
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3

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    I don't see a vent. The main stack is a couple of feet away and each of these drain lines have separate connections to the main stack. Was this ever up to code (built in the late 60s) or just a hack plumbing job?

  4. #4
    In the Trades Gary Swart's Avatar
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    In addition to what Jim just posted, a DW drain is supposed to connect to the sink drain via the disposal if you have one or via a special wye tail piece the connects to the sink drain. In addition, the DW drain line should be connected to an air gap on top of the counter to prevent a backflow of contaminated water from the sink drain from getting into the DW. Some places allow a high loop of the DW line that loops above the DW. It looks like you have somewhat of a handyman version of a high loop. You definitely need to rework the entire sink drain to comply with code. The S trap is illegal everywhere.

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