what is up with this drain backup

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by happydude45, Nov 22, 2009.

  1. happydude45

    happydude45 New Member

    Messages:
    2
    Location:
    Ontario
    I have attached a diagram of the system. The basement sink drains very very slowly, and gurgles loudly when using the upper sink.

    Actions taken so far with no success:
    - snaked from basement sink to where the pipe goes into basement floor (at the red marker - i cut into it at this point and verified that there was no clog upstream to sink)
    - snaked downward 20' to 25' below ground with my 3/8" snake, came up with a bit of hair, but can't be sure if there is a clog down there.

    I am hoping the problem is a clog in the vent, otherwise it must be a clog underground??...

    thanks for your help!

    Attached Files:

  2. nhmaster

    nhmaster Master Plumber

    Messages:
    3,189
    Location:
    S. Maine
    It's probably clogged underground and a 3/8 snake is next to useless.
  3. Terry

    Terry Administrator Staff Member

    Messages:
    15,418
    Location:
    Bothell, Washington
    You have run two sinks on the vertical without proper venting.
    Anytime you drain the top sink, it will pull water from the lower sink trap.

    [​IMG]
  4. happydude45

    happydude45 New Member

    Messages:
    2
    Location:
    Ontario
    Yes I know the plumbing system is not done properly. It wasn't me, just a gift that came with the house!


    I should add that when I run lots of water in the upstairs sink, water will actually come out the lower sink drains! In other words, the air is pushing out. Later it starts gurgling "the other way" as it tries to pull air in, as the water slowly drains back down.

    does that provide more evidence for a clog underground?
    any tips on how to add a vent to improve the system?
  5. Doherty Plumbing

    Doherty Plumbing Journeyman & Gas Fitter

    Messages:
    810
    Location:
    Penticton, BC
    As long as the pipe shown coming off the top of the highest sinks connection to the stack is a vent then you're fixtures would be vented properly as far as I know about your code down there.

    You would be simply wet venting the bottom sink.

    To remedy the situation you should run a snake from the roof down through the venting and down to larger piping (like a 3 or 4" connection). Flush water through the sinks as well.

    Be careful because if you DO knock out a bunch of gunk to the lowest point on the vertical soil-or-waste stack you could create a temporary blockage at the bottom and flood out the lowest sink ... until the snake gets there.
  6. Terry

    Terry Administrator Staff Member

    Messages:
    15,418
    Location:
    Bothell, Washington
    When an upstairs sink is above a downstairs sink, on the same line, then yes, it overflows the lower sink.

    I run into that all the time with handman jobs.

    Wet venting is only allowed with fixtures on the same floor, and they need to be sized for that.
  7. Doherty Plumbing

    Doherty Plumbing Journeyman & Gas Fitter

    Messages:
    810
    Location:
    Penticton, BC
    Wow really you guys can't wet vent vertically like that? Didn't know that!

    :cool:
  8. nhmaster

    nhmaster Master Plumber

    Messages:
    3,189
    Location:
    S. Maine
    Nope. you can stack vent like that though provided the stack is large enough and has no offsets.
  9. Terry

    Terry Administrator Staff Member

    Messages:
    15,418
    Location:
    Bothell, Washington
    So if it's working so well, then why is the lower sink having problems?
  10. Doherty Plumbing

    Doherty Plumbing Journeyman & Gas Fitter

    Messages:
    810
    Location:
    Penticton, BC
    Would this be acceptable to you guys? A little off topic i know heh.

    [​IMG]
  11. nukeman

    nukeman Nuclear Engineer

    Messages:
    711
    Location:
    VA
    I have the same situation in my house. Two lavs on the 2nd floor draining into 2" copper. This line becomes the vent for the basement lav. Currently, I don't have any problems with it, but I do know it is against current code. I don't know why they didn't just run the 2nd floor lavs into the 3" waste line for the WC. The 3" is only about 16" away from the 2". Probably won't be able to do anything about it until I renovate the 2nd floor bath sometime in the future.

    Good luck, happydude. Hope you get it figured out. :)
  12. FloridaOrange

    FloridaOrange Plumbing Designer

    Messages:
    1,317
    Location:
    SW Florida
    Yes, that would be code legal here. I thought that the vent would be equal to the size of the drainage portion but didn't see it on a quick review of the code....then again, the geniuses have now begun to allow cpvc (with fittings) under slab.
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