Required drain size for double sink and tub

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by boomer70, Sep 13, 2006.

  1. boomer70

    boomer70 New Member

    Messages:
    12
    What is the required drain diameter for a double sink (back-to-back) with a tub downstream?

    Thanks for your help.
  2. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,650
    Location:
    Cave Creek, Arizona
    pipe

    It depends on how you do the piping, but normally 2".
  3. boomer70

    boomer70 New Member

    Messages:
    12
    On the second floor of a two-story house, two lavs are at the beginning of a drain line. They are connected with a double sanitary tee and are branch vented with 1 1/2" pipe to the stack vent. The 1 1/2" drain runs 2-3 feet to the soil stack that serves the second floor. Note that a watercloset drains directly into this soil stack as well and that the soil stack is also branch vented to the same stack vent that the lavs are vented to.

    A tub is being added, and the drain needs to connect to the soil stack without taking too many bends. Can the tub drain connect to the existing 1 1/2" drain line coming from the double lavs?
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