dishwasher drain directly into waste line

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by mjbraun, Mar 10, 2009.

  1. mjbraun

    mjbraun New Member

    Messages:
    6
    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?
  2. SewerRatz

    SewerRatz Illinois Licensed Plumber

    Messages:
    1,705
    Location:
    Chicago, IL
    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.

    [​IMG]
    Last edited by a moderator: Jan 17, 2012
  3. Terry

    Terry Administrator Staff Member

    Messages:
    15,316
    Location:
    Bothell, Washington
    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.

    [​IMG]
    Last edited: Jan 28, 2011
  4. Violin

    Violin New Member

    Messages:
    11
    Location:
    New Jersey
    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!
  5. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,062
    Location:
    Cave Creek, Arizona
    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: Sep 23, 2010
  6. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Many dishwashers these days have a 'high loop' in the drain hose, fixed right along the side of the drum.
  7. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    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.
  8. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,062
    Location:
    Cave Creek, Arizona
    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.
  9. benze

    benze New Member

    Messages:
    63
    Location:
    Montreal, Canada
    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
  10. Redwood

    Redwood Master Plumber

    Messages:
    7,450
    Location:
    Connecticut
    The air gap is to prevent sewage from flowing under pressure into the dishwasher in the event the drain line clogs.
  11. Violin

    Violin New Member

    Messages:
    11
    Location:
    New Jersey
    [​IMG]


    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 a moderator: Jan 17, 2012
  12. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,062
    Location:
    Cave Creek, Arizona
    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. Violin

    Violin New Member

    Messages:
    11
    Location:
    New Jersey
    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. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,062
    Location:
    Cave Creek, Arizona
    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.
  15. Inspektor Ludwig

    Inspektor Ludwig Journeyman/Inspector

    Messages:
    167
    Location:
    In the good ol' UPC
    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.
  16. Violin

    Violin New Member

    Messages:
    11
    Location:
    New Jersey
    Yep - I was able to find that name on the interwebs. I haven't found anyplace that sells it online. I'll take a drive over to my local supply house and see if they carry it. Does anyone know where to buy one online?

    This is what the outside looks like:

    [​IMG]

    If I could easily connect the dishwasher to the sink drain I wouldn't be researching this. Our design has the sink and dishwasher on adjacent walls, separated by a corner cabinet so there's about six feet of wall between the sink and dishwasher.

    Even if our code doesn't require an air gap (and I doubt that it does because I never see one above the counter in anybody's kitchen around here) I can see the logic of having one. It would have to be one heck of a backup as the kitchen is on the second floor of a split level and there are fixtures in the basement and on the first floor. Still, I eat on the dishes that come out of that dishwasher and if I can prevent contaminating the dishwasher for a couple of bucks and a few extra minutes of install time, its worth it to me.
  17. Violin

    Violin New Member

    Messages:
    11
    Location:
    New Jersey
    Supply house says air gaps haven't been required here for a while and they don't carry Johnson Tees.
  18. you can make one with a 3/4" tee. A cap is a screen to prevent bugs from entering. You cap it yourself.

    what i cannot figure out is why one "needs" to plumb that copper line down to the floor. This looks optional to me.
  19. The Fisher & Paykel diagram is a stand pipe. Air gaps and stand pipes are the same (they are indirect drains).
  20. shacko

    shacko Master Plumber-Gas Fitter

    Messages:
    561
    Location:
    Rosedale, Md
    >>>As far as I know there are only a few states that require an airgap on a dishwasher, Washington and California.<<<

    If you are working under an unmodified UPC code you have to have an air-gap.
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