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Thread: dishwasher drain directly into waste line

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    Default dishwasher drain directly into waste line

    My dishwasher will not be directly beside my kitchen sink. I would like to run the drain down thru the floor and into the same waste line that my sink drains into (this would be tying into that waste line after and below the kitchen sink). Where could I find a diagram (or photo) illustrating how to do this correctly?

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    Illinois Licensed Plumber SewerRatz's Avatar
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    I never met a plumbing inspecter that allowed the dishwasher to drain to a lower level. But he has allowd the dishwasher to be installed as pictured.

    Last edited by Terry; 01-17-2012 at 02:16 PM.

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    Forum Admin, Expert Plumber Terry's Avatar
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    I would like to run the drain down thru the floor and into the same waste line that my sink drains into (this would be tying into that waste line after and below the kitchen sink). Where could I find a diagram (or photo) illustrating how to do this correctly?
    No legal way to do that.
    Most places require an air gap or at least a high loop before entering the drain.
    I've installed many like the picture above, and also an air gap into a disposer. Some places let you "high loop", but nobody allows connection without those measures below the floor.

    Last edited by Terry; 01-28-2011 at 01:09 PM.

  4. #4

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    SewerRatz -

    Great photo!

    This setup is perfect for my kitchen remodel as the dishwasher and sink will be on adjacent walls.

    What's the minimum size for the copper pipe?

    I assume there is some type of brass fitting to clamp the dishwasher hose to but I can't tell from the photo. What should I use there?

    (I realize that this is an old thread - others please weigh in.)

    Thanks!

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    Moderator & Master Plumber hj's Avatar
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    If you "gravity drain" a dishwasher which was not intended to drain that way, (and I have not seen any since the 50's that were), the dishwasher will not hold water. And guess what would happen inside the dishwasher when the sink drain plugged and backed up.
    Last edited by hj; 09-23-2010 at 06:08 AM.

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    Plumber jimbo's Avatar
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    Quote Originally Posted by hj View Post
    If you "gravity drain" a dishwasher which was not intended to drain that way, (and I have not seen any since the 50's that were), the dishwasher will not hold water.
    Many dishwashers these days have a 'high loop' in the drain hose, fixed right along the side of the drum.

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    Plumber jimbo's Avatar
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    Quote Originally Posted by A. Nicholas Fivepennies View Post
    SewerRatz -

    Great photo!

    This setup is perfect for my kitchen remodel as the dishwasher and sink will be on adjacent walls.

    What's the minimum size for the copper pipe?

    I

    Thanks!
    You should use 3/4" copper. Note that the copper connects to a TEE, and the 'air gap' connection goes out through the outside wall.

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    Moderator & Master Plumber hj's Avatar
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    If that is the case, I would not say "many", because all of the ones I have installed still have the DRAIN hose going from the pump directly to the final connection. They ALL have high loops in the water line, however.

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    DIY Member benze's Avatar
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    This may sound like a silly question, but does the tall vertical vent pipe not perform the same effect as the air gap? I'm a little confused for the reason why an air gap is needed; I always thought it was to help with the venting of the dishwasher. But with the 3/4" copper pipe dumping into a 1 1/2" standpipe, I would have thought / expected that there wouldn't really be any need for any additional venting at that point.

    Thanks,

    Eric

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    Master Plumber Redwood's Avatar
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    Quote Originally Posted by benze View Post
    This may sound like a silly question, but does the tall vertical vent pipe not perform the same effect as the air gap? I'm a little confused for the reason why an air gap is needed; I always thought it was to help with the venting of the dishwasher. But with the 3/4" copper pipe dumping into a 1 1/2" standpipe, I would have thought / expected that there wouldn't really be any need for any additional venting at that point.

    Thanks,

    Eric
    The air gap is to prevent sewage from flowing under pressure into the dishwasher in the event the drain line clogs.

  11. #11

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    One of the recommended installation methods for mine (Fisher & Paykel) shows the drain hose being looped up high and inserted into a standpipe. I'm guessing that would eliminate the need for an air gap, but it looks like its asking for trouble. I'd rather a backup be directed outside than into an adjacent cabinet.
    Last edited by Terry; 01-17-2012 at 02:20 PM.

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    Moderator & Master Plumber hj's Avatar
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    That is a "stupid" method of connecting the sink and is guaranteed to flood the cabinet sometime in the future. It is what happens when engineers come up with "brilliant ideas" without knowing what they are doing.

  13. #13

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    That's what I figured. I think I'll go with SewerRat's setup above.

    What does that look like outside of the house? - Just a PVC pipe sticking out of the wall, (mine is vinyl siding) or is there something more outside?

    Finally, if I use 1 1/2" PVC for the drain, what size pipe should I use to run outside? I'm guessing 3/4".


    I can't thank you all enough.

  14. #14
    Moderator & Master Plumber hj's Avatar
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    That is a specific fitting made for that purpose. I have seen pictures of it, but have never seen one in a supply house. Originally it was NOT an approved device since they did not want to pay the expensive cost of having it tested, so inspectors would not approve its use. That may have changed since then if it is available in Chicago.

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    Journeyman/Inspector Inspektor Ludwig's Avatar
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    That little do-hicky is a "Johnson Tee" that serves as the air gap but it drains to the outside of your house and eliminates that extra hole in the countertop. It's basically a 3/4 x 1 1/2 x 1/2 tee. The portion that sticks outside of your house is a 3/4" piece of plastic pipe that would have cap on the end with holes drilled into it. As far as I know there are only a few states that require an airgap on a dishwasher, Washington and California. I believe, but I may be wrong, that most states allow you to do a high loop under the cabinet and connect to the disposer. I'd find out if your state/city requires and air gap first then go from there.

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