Reducing sink drain from 2" to 1.5

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by chris989, Jun 14, 2020.

  1. chris989

    chris989 New Member

    Joined:
    Mar 18, 2018
    Location:
    idaho
    Hello all,

    Yes i know that reducing drain waste in the direction of flow is a violation.

    I have a circumstance where a 2" trap arm (40") is used to drain a single sink. The trap arm goes into a standard 2x1.5x2 san-tee. Due to a 70s home and very limited space, reducing back to 1.5 on the vertical drop would make life a lot easier.

    There is very limited space and a semi butchered 2x4 top plate to work with. When i build I always frame 2x6 for any wall calling plumbing but this time i do not have that luxury.

    All said,,, I would not think on a vertical drop the reduction would be a worry, It has no solids, no disposal etc.

    Thanks,
    Chris
     
  2. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    [​IMG] Is this the standard santee you are talking about?
     
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  4. chris989

    chris989 New Member

    Joined:
    Mar 18, 2018
    Location:
    idaho
    Yes, 2 inch for trap arm, 2 inch drain, 1.5" vent. I was considering bushing the drain back to 1.5 as it turns through a few joist and through a top plate. It then would go back to 2".

    THe more i talk about it the worst it sounds. I will squeeze in there next week and see if i can not make 2" work
     
  5. plumber01

    plumber01 In the Trades

    Joined:
    May 13, 2015
    Location:
    Washington
    If it is just a lavatory sink there is no problem running an 1.5" drain, trap arm and vent.

    But yes, if you reduce the drain to 1.5", you need to reduce the trap arm to 1.5". 42" max trap arm.
     
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