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Discuss Dishwasher Waste Help in the Plumbing Forum area at

  1. David Usher

    David Usher New Member


    I'm installing a dishwasher into a new kitchen as part of a new build (no kitchen there before). I installed a 40mm waste pipe within the joists (first floor kitchen) into the soil pipe with a Boss strap-on. The 40mm pipe appears through the floor vertically (standpipe) to connect up to a dishwasher located in a breakfast bar (not near the sink).

    I didn't add a trap under the floor :/ (see pic attached)

    Could I cut the 40mm pipe and connect to a standpipe trap just above the floor - attach to one of these (see drawn pic attached) -

    Should I get a tapered appliance fitting for the top of the standpipe or just pop the dishwasher waste outlet into the standpipe?

    Would appreciate some advice - many thanks.


  2. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Hep20 trap ?
    • Agree Agree x 1
  3. snowhead

    snowhead Plumber

    • Agree Agree x 2
  4. David Usher

    David Usher New Member

    Thanks guys, great help - any preference on positioning the valve on the vertical pipe?

    Is it also safe to just push the flexible waste pipe from the dishwasher into the larger waste pipe?
  5. Roy_66

    Roy_66 Member

    I'm just a DIYer (but retired to compensate for my slowness):

    If you go for the valve, then I'd get the tapered connector you mentioned so all sealed, and some pressure then to make sure valve opens. . . at least for a certain length of history

    If you go for the stuffed in the top of the standpipe (and simple Hep trap) I'd want it stuffed in about a foot and fixed with a clip, and make the standpipe as tall as you reasonably can. Don't cut off for the trap too near the floor (might want to remake one day). Sorry I don't have one now to photo but that is what I would do, being old fashioned (easy to maintain). The more head you can get will help stop minor dirt building up in the trap and hence avoid floods. Cunning trick is to keep an old wash up bowl etc. under it so come the day it blocks up and starts to overflow, you won't have soggy chipboard before you realise.

    Think about which you prefer to maintain downstream. Not sure if, like wash machines it probably will want cleaning out every so many years (depending on what machine cleaners etc. you might use). I'm not sure if dishwashers not as bad as washing machines for gumming up the waste.

    Do modern dishwashers detect the output is blocked and shutdown with helpful error code? Hmmmm . . .

    Not helpful here but cunning plan (for non-islands) sounds to put your boiler condensate pipe into same trap as a washing machine then the acid from the boiler helps clean away the alkaline output from the washer. I'm only two years down the line on that setup (not done by me) fingers crossed :) .

    Somebody will now tell me the real reason why technically after years of standpipes they changed to the direct connection :)

    • Like Like x 1
  6. David Usher

    David Usher New Member

    Thanks Roy - great advice.
  7. Darren Jackson

    Darren Jackson Plumber GSR

    I personally would go for the standpipe (hockey stick) like your drawing. Mainly because the self closing valves when used on appliances with food waste going through them can and often do become stuck and then do not shut off properly, letting foul smells from the soil pipe enter the room.
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