dumb question about under sink plumbing

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by qgsm33, Jul 16, 2012.

  1. qgsm33

    qgsm33 New Member

    Messages:
    6
    Location:
    Texas
    Hi folks - apologies in advance for what you may find is a dumb question. I've got a sink in a 2nd floor bathroom that's plugged. took the P-trap off and the trap was fairly clean...but when I looked into the drain connection in the wall, you can see water standing in the drain pipe inside the wall. The bath tub located next to the sink drains fine...and i'm assuming they share a common drain pipe heading downstairs. If true, I'm guessing the plug is not too far below where the sink drain goes into the wall.

    Here's where I'm a little confused: when I was looking into the drain line in the wall, I could see the connection was a tee: one branch going down and the other going up. I'm assuming the part going up is the vent line. What I also noticed though was that there's another line that tee's off of the sink drain just above the p-trap. Looks like about 3/4 inch PVC that runs pretty much horizontal, makes a 90 degree turn, and then heads into the way. What the heck is this? I'm guessing it's another vent line??? Is this a normal practice???

    Because it runs horizontal for about 12" then turns 90 degrees and runs another 12" horizontally, I'm guessing it's prone to clogging also (once the sink drain starts backing up)??? I'm attaching some pics that hopefully show what I'm seeing...

    Thanks in advance for any explanation... 2012-07-16_22-13-46_641.jpg 2012-07-16_22-14-01_975.jpg
  2. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    The PVC line tying in is most likely a drain from the air conditioner evaporator coil.
    You should NOT see water on the Tee inside the wall.
  3. qgsm33

    qgsm33 New Member

    Messages:
    6
    Location:
    Texas
    bingo!

    Bingo! that smaller PVC line was in deed coming from the air conditioner unit in the attic. I flushed some water down the line from above and no problems there. Pulled a major hairball/clog out of the drain line in the wall (with my handy dandy hand-cranked snake). Clog was about foot and a half down the wall... Thanks for the quick response and help Jimbo...
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