Use of 90 Degree Elbow (not vent elbow) for Vertical to Horizontal Drain

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by emazz1, Feb 13, 2021.

  1. emazz1

    emazz1 New Member

    Feb 13, 2021
    Need some advice for a first time DIY plumber here.

    I'm roughing in drains for a double vanity. I'm using 1.5" drains from each traveling horizontal in the wall to meet a 1.5" vertical drain, with a vent going up from that. The bathroom has a 3" waste pipe that runs perpendicular to the vertical lav drain pipe, but is not directly below it. Can I use a 90 degree elbow or a 90 degree long sweep at he bottom of the vertical drain to then tie into a wye I'm adding to the 3" waste pipe?

    Staring at the sink wall, the vertical drain would hit the 90 degree elbow and come straight out towards you, and then tie into the 3" waste pipe. Is the 90 appropriate?
  2. breplum

    breplum Member

    Oct 2, 2004
    Plumbing and heating contractor
    San Francisco Bay Area
    For vertical to horizontal drainage, a long sweep 90 IS the fitting to use.
    When more than one lav drain, two inch pipe should handle the combined load. Inch and a half is fine for combined vents.
    When horiz. drain connects to vertical, a Tee fitting is used. Unnecessary to use a WYE.

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  4. emazz1

    emazz1 New Member

    Feb 13, 2021
    Thanks breplum. So if I have a lav sink on each side of the vertical drain, I would use a double sanitary tee to meet in the middle, with my vent going up, correct? Also, after I use the long sweep 90 to transition from vertical to horizontal, does it matter if I use a wye or a long sweep to tie into my 3" horizontal drain pipe?
  5. Tuttles Revenge

    Tuttles Revenge In the Trades

    Oct 15, 2014
    A wye or Combination wye&1/8th bend / Long sweep tee (as the box stores call them) are both appropriate. The combi is a wye with a 45 to make it the long sweep.
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