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Thread: Installing new kitchen sink, why are there two wall drains?

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  1. #1
    DIY Junior Member Nina in Florida's Avatar
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    Default Installing new kitchen sink, why are there two wall drains?

    I have been hating my undermount dual compartment stainless sink for 8 years since I installed it. I have recently bought a big Kohler Vault sink. Its a drop in single compartment with the micro edge.

    So now I know more about home improvement than I did when I bought this house. Thanks to the Internet. And I'm going to buy a new disposal since the Badger 5 isn't leaking yet, but is rusty. and I'm looking under the sink and I can't figure out why there are two drain in the wall under the sink.???

    I'd like to attempt the plumbing of the new drain and disposal, but I'm not sure which drain to use? One is higher than the other.

    Is one for the dishwasher? Do I need to add a p trap if I use that drain for the dishwasher? What about a air gap? I'm in Florida and you never see them here.

    Is there any advantage to the dishwasher drain going into the disposal? I'm thinking the disposal could collect and chew up any food particles in the dishwasher?

    I can post a picture, but its not that complicated. Seems when the house was built in the early 80's, a dishwasher was expected because I have 4 angle valves under the sink. So is that what the second drain is for?

    Any tips or location of diagram on how to do it correctly will be appreciated

    Single white female in Florida

  2. #2
    Moderator & Master Plumber hj's Avatar
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    The top one is the drain, and the bottom one is a "cleanout" which is not supposed to be used for a drain.
    Licensed residential and commercial plumber

  3. #3
    Retired Defense Industry Engineer jadnashua's Avatar
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    IF they are stacked vertically one on top of the other, then they're as HJ said...IF they are separated horizontally, they may have just put in two traps. If it's two traps, you can cap one if you wish. OFten when replacing a sink the height of the connection in the wall is no longer usable if it is to high. You may need to rework the pipe. As to an air gap, that is the safest way to install a DW. It is required is some places, and recommended everywhere. But, your local code may allow only a high loop. IF you're going to install a new disposer, use the inlet on that for the DW, it's the easiest way and works fine.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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