Adding a utility sink - Will this work?

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by Sylvester, Jan 31, 2014.

  1. Sylvester

    Sylvester New Member

    Messages:
    5
    Location:
    Maryland, USA
    Hi everyone. Here's another "can I do this" thread. :)

    I want to add a utility sink into my basement. Ideally, it will be positioned next to the washer and dryer, and I would like to tie it into the existing drain line from the washer discharge. It currently has 2" Sch. 40 PVC washing machine standpipe and P-trap, going to a Sani-Tee and drain with an AAV on the top, like this (pardon my horrendous drawing):

    plumbing.jpg

    I want to add the sink between the washing machine and the Sani-Tee. I'm thinking Sch. 40 P-trap, trap arm going to a 90 elbow that connects to a combo wye added to the existing drain line. Like this:

    plumbing2.jpg

    Will this work? Is it legal? And will it vent properly? I'm not sure if I'd have to add another AAV between the sink trap and the combo wye. Thanks!
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
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    Location:
    New England
    The sink trap will get sucked dry when the WM drains.
  3. cacher_chick

    cacher_chick Test, Don't Guess!

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    Location:
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    What you have drawn is not permitted. You can install another sanitary tee over the existing one and run your sink to it. Both the washer and the sink should be 2" pipe, and the trap to vent distance cannot exceed 5' if it is under UPC.
  4. Sylvester

    Sylvester New Member

    Messages:
    5
    Location:
    Maryland, USA
    Cacher_chick, is it not permitted to tie in to the existing WM drain, period? Or just because of the siphoning issue?

    I clearly see what you mean now, Jadnashua.

    Another concern I have is, looking at things now, I might not have the vertical clearance I need anyway. The bottom of the P-trap might be at the level of the existing horizontal drain run. Could I flip-flop the arrangement, and do this?
    plumbing3.jpg
  5. Gary Swart

    Gary Swart In the Trades

    Messages:
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    Location:
    Yakima WA
    You have not one but two illegal S traps. Vents must be in the trap arm prior to the arm turning downward.
  6. Terry

    Terry Administrator Staff Member

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    [​IMG]

    Putting the sink above the washer works best.
    The washer will always siphon a sink if the sink is below.
  7. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
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    Location:
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    They are NOT "S" traps unless they are connected to the vertical line with Ys or combos. The sink can connect to the horizontal line if the trap is PROPERLY vented. You cannot connect the sink the vertical line UNDER the washing machine, unless you properly vent the sink line to prevent both positive and negative pressures, which means, but definition, you cannot use an AAV.
    Last edited: Feb 1, 2014
  8. Sylvester

    Sylvester New Member

    Messages:
    5
    Location:
    Maryland, USA
    Forgive me, my morning coffee is still trying to work in. I thought the S-trap was defined by having too short of a trap arm (not 2x the diameter), not necessarily by its venting.
  9. cacher_chick

    cacher_chick Test, Don't Guess!

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    Location:
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    Gary is mistaken. You should be able to lower the sanitary tee for the washer so that the washer trap is lower, and the sanitary tee for the sink will go above the washer's. You do not want a major drain over the top of a minor one.
  10. Sylvester

    Sylvester New Member

    Messages:
    5
    Location:
    Maryland, USA
    To connect the sink to the horizontal line, could I vent the trap arm with an AAV? Given the location, I do not have another way to vent.
  11. cacher_chick

    cacher_chick Test, Don't Guess!

    Messages:
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    Location:
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    You could do that, but both of the AAV's need to be installed higher than the flood rim of the higher fixture. Not doing so will cause the AAV's to fail if a backup of laundry suds comes up the vent.
  12. Sylvester

    Sylvester New Member

    Messages:
    5
    Location:
    Maryland, USA
    Ok, great. Now, if I did it the other way - basically as I drew most recently but with the sink draining ABOVE the washer - that will be a wet vent of the washer, yes?
  13. cacher_chick

    cacher_chick Test, Don't Guess!

    Messages:
    3,244
    Location:
    Land of Cheese
    Correct- it is a vertical wet vent, which is a common practice with a washer and utility sink.
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