Horizontal pipe size for kitchen and laundry

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Rocknroj, Dec 19, 2019.

  1. Rocknroj

    Rocknroj Member

    Dec 30, 2008
    I am wondering if I should upsize an existing 2" horizontal (ABS), nicely pitched that serves both my kitchen and clothes washer.. There is a new 2" wash machine drain. 1 1/2 kitchen, running horizontal then connected
    to a 2" line that runs about 30 ft before connecting to 3".

    based on fixture units i realize that the 2" is fine. As a matter of practice should the 2" be upsized to 3"? Or is 2" better than 3" for keeping the pipe clean?


    thanks in advance
  2. Terry

    Terry Administrator Staff Member

    Aug 17, 2004
    Bothell, Washington
    Washington State with UPC code is okay with 2" for a sink and washer.
    Some codes like to see 3".

    Sinks are 2" with a 2" cleanout and 1.5" for trap and vent.
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