Adding second sink on same drain

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by lumberguy, May 3, 2009.

  1. lumberguy

    lumberguy New Member

    Messages:
    2
    Hi,
    I am working on remodeling our kitchen but would like to add a prep sink with a g-disposer about 10 ft away from the main sink with a g-disposer. We have a full basement so all the drain pipes are exposed so easy to work on but my question is my main sink drains into a 1 1/2" cast iron pipe that goes under the foundation of the house and meets up with the main 4" drain under my back yard. Is it ok to connect two sinks on a 1 1/2" drain pipe? If not, is there something else I can do to conform with code to make this possible? We are still in the design stage of the kitchen and this would be a game-changer in the design, so I need to know if this can be done by washington state code

    Thank you ahead of time

    Steve
    Last edited by a moderator: May 3, 2009
  2. Terry

    Terry Administrator Staff Member

    Messages:
    14,766
    Location:
    Bothell, Washington
    Normally there is a 2" hub close by that the 1.5" comes out off.
    I would look for that.

    Kitchen sinks use 2" now, and the trap arm and trap can be 1.5"
    Two sinks will need 2"
  3. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,253
    Location:
    Cave Creek, Arizona
    drain

    THere were few 1 1/2" cast iron drain lines installed, so your sizing may be off. I am guessing that the drain part of the equation will be the easy part. What will you do for a vent?
  4. Terry

    Terry Administrator Staff Member

    Messages:
    14,766
    Location:
    Bothell, Washington
    The longest trap arm before the vent in Washington is 42"

    Each sink will need to be vented as hj mentioned.
  5. lumberguy

    lumberguy New Member

    Messages:
    2
    Pipe dia.

    I don't know what the ID of the pipes are but I measured the OD of the vertical pipe going into the foundation from the sink at 1.900". Right before it goes into the foundation it couples with another pipe and the OD of the exposed coupler is 3.650" (so maybe that is 2") The house was built in 1943 so it may have been up to code back then.

    As for the venting we will have the room gutted and we should be able to add a vent straight up the wall and through the roof...would all this work?

    Thanks again
    Steve
  6. kingsotall

    kingsotall Plunger/TurdPuncher

    Oh, so it's not on an island but there will be a wall behind the sink¿
  7. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,253
    Location:
    Cave Creek, Arizona
    drain

    It was not so much a matter of code to not use 1 1/2", it was just that we did not like working with it.
  8. SewerRatz

    SewerRatz Illinois Licensed Plumber

    Messages:
    1,706
    Location:
    Chicago, IL
    You can run the vent up the wall and tie it in with the same vent for the kitchen sink, or tie it in with any vent in the attic.
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