advice on new kitchen sink drain

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by briz, Jul 9, 2012.

  1. briz

    briz New Member

    Messages:
    4
    Location:
    b-c
    I am going to be installing a kitchenette in my basement and would like some advice with the drain pipe for the sink. On the picture, you can see the main drain is vertical and comes from the bathroom on the floor above. The small horizontal pipe is the drain from the kitchen also, one floor above. The new kitchenette sink drain is behind that wall, one foot to the left of the main drain. My new drain cannot be higher than the horizontal drain, so that presents a problem. Not sure if I need to vent the new drain, as it would only be a distance of two feet from the main drain.
    Appreciate advice on my options here, and how to proceed with the job.
    Thanks

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  2. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,689
    Location:
    Cave Creek, Arizona
    the distance from the main drain usually has little bearing on whether you need a vent or not. In this case you WILL need a vent of some kind.
  3. Terry

    Terry Administrator Staff Member

    Messages:
    15,053
    Location:
    Bothell, Washington
    I second that. You will need a vent for the lower kitchen sink when you add it.
    Having a fixture connect to a waste stack without a vent inbetween means either you will be siphoning the trap, or pressure down the pipe can force gooey, slimy water into your kitchen sink anytime someone flushes a toilet upstairs.
  4. briz

    briz New Member

    Messages:
    4
    Location:
    b-c
    Thanks for the reply.
    So can I cut the vertical line and connect my new drain line into that? Also, thinking about an auto-vent for that drain. Would that be a good way to go, as it seems more simple.
  5. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,689
    Location:
    Cave Creek, Arizona
    Autovents are a poor choice for a lower level fixture, because water flowing down from the upper levels can create a positive pressure and an aav CANNOT relieve positive pressures.
  6. briz

    briz New Member

    Messages:
    4
    Location:
    b-c
    Thanks HJ,
    Do you have any venting suggestions instead of the autovent for this application?
  7. mikeplummer

    mikeplummer Plumber

    Messages:
    190
    Location:
    Ontario, Canada
    an autovent isn't a good choice there because they do not protect the trap from backpressure, as Terry described. you should run a vent line up to the next floor and needs to tie in above the highest fixture this stack serves
  8. briz

    briz New Member

    Messages:
    4
    Location:
    b-c
    So, can I use the existing vertical drain to connect to?
    Thanks
  9. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,059
    Location:
    New England
    You can connect the new sink into that vertical drain, BUT, you need to run a new vent 42" above the floor or 6" above the highest thing that drains into it. You don't need to run a new vent to the roof, and the attic may be a choice.
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