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Thread: Kitchen and bath sink to 3" waste line

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  1. #1

    Default Kitchen and bath sink to 3" waste line

    Scenario: 3" drain that will connect to 1st floor toilet. kitchen and bathroon sink upstream from the 3" waste line. No disposal, dishwasher to be installed. Kitchen and bath 1 1/2" drains are vented at each location.

    Best connection is:

    A. Connect kitchen and bath with 1 1/2" 'Y' then run single 1 1/2" line to 3" drain connecting in a 3 X 3 X 1 1/2 T after toilet 90 deg. Toilet waste would then be in the 3" line before sink drain connection to the 3" sewer line.


    B. Extend 3" waste line beyond the toilet, connecting the toilet with a T, then connect the 1 1/2" bath and kitchen sink lines to the 3" sewer line.

    Runs: From kitchen to Kit/bath 1 1/2" T connection would be 6 1/2'.
    From bath sink to Kit/Bath 1 1/2" T would be 5 1/2'
    Kit/Bath 1 1/2" T to 3" Y connectionis less than 2'
    Toilet waste flange to vertical waste sewer is 3 1/2'

    All runs will have 1/4" per ft slope.

    Thanks you all for your time monitoring these forums and your excellent advise.

    Thank you,
    VT David

    formerly of NH

    Diagrammed PIC

    Last edited by VT David; 01-07-2007 at 11:07 AM.

  2. #2
    Plumber solsacre's Avatar
    Join Date
    Nov 2006


    alright.... alot of that depends on local codes.... but I would never run a kitchen line less than 2". It's easy to pay a plumber (tell him or her what you want) an hour ($70?) to give you good local advice.

    good luck


  3. #3


    This is a modular home and the kitchen line through the wass to the basemet where it will connect is 1 1/2". Should I reun 2 " from there.

    Building codes; none around here! Which is why i would like to know best practice on this design. Thanks

  4. #4


    My little brain will not picture all of that at one time. I need a picture/drawing. Doodle one with "paint" then post it to photobucket.com and put it on here. My opinion, and what I've learned by reading this board is that the line to a shower or washing machine should be 2", the stand pipe for the washing machine could be 1 1/2". A tub is okay with 1 1/2". I'd question whether or not you could run all together on the same 1 1/2" line before going into a tee on 3". It would work if you didn't release water in too many at the same time... that's why you need to run them into a bigger line. As for where the tee in the 3" needs to be I don't know that it matters, all are going to the same place.

  5. #5

  6. #6
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    Kitchen drain lines should be 2"...
    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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