What the heck is this?!?!

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by stillad, Sep 18, 2009.

  1. stillad

    stillad New Member

    Messages:
    3
    Location:
    Huntsville, AL
    Ok, here's what i've got under my kitchen sink (see pic).

    photo (2).jpg

    I'm installing new countertops with an undermount sink. However, the PVC loop you see in the background (on the right, behind the main drainage line) is going to cause some interference with my new deeper sink.

    I can't find anyone who can tell me what this loop does. It looks similar to a yoke vent except that it feeds back into the main line without an "exhaust line" venting outside.

    Do i need to keep it? If i lower it on the top end by a few inches is that going to cause me any problems?

    Thanks for any help!

    PS - I'm on a slab. Don't know if this will make a difference to any recommendations but thought it might be relevant. House was built in '84.
  2. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,387
    Location:
    Yakima WA
    Sure looks strange to me too. Perhaps one of the pros will be able to shed some light on it. If it was mine, I'd get rid of it. I can't see that it is doing anything except taking up space.
  3. FloridaOrange

    FloridaOrange Plumbing Designer

    Messages:
    1,317
    Location:
    SW Florida
    That's an island vent loop. It's done incorrectly though as far as I can tell.

    [​IMG]

    You might want to consider correcting that.
    Do you have an accessible wall to run a new vent up through? You may be able to use an AAV but that depends on your local codes.
    Your drains for your new sinks will be lower so you are going to have to modify your plumbing anyway.
    Last edited: Sep 18, 2009
  4. stillad

    stillad New Member

    Messages:
    3
    Location:
    Huntsville, AL
    Unfortunately, no. I suppose it's possible, but given the exceedingly difficult requirements (slab, vent line would have to be run through exterior wall, etc) and that fact that I've not had any drainage problems yet, I'm trying to find another option.

    I'll have to look into that AAV thing. Thanks.
  5. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,060
    Location:
    Cave Creek, Arizona
    drain

    It is some handyman's attempt to do a cheap version of a yoke vent. It is completely ineffective most of the time, but will prevent siphonage at the very end of the drain cycle when the pipe is not full of water. Lowering it will not damage its effect because any stoppage is going to be below the "Y" so it will not create a secondary drain path.
  6. nhmaster

    nhmaster Master Plumber

    Messages:
    3,189
    Location:
    S. Maine
    It does nothing at all because #1 it's wrong and #2 the trap attached is a S trap which will siphon with or without it.
  7. johnjh2o1

    johnjh2o1 Plumbing Contractor for 49 years

    Messages:
    1,143
    Location:
    South*East
    In are area we are allowed to use studor vents on island sinks. They work very well. It would be installed just above the 2x1-1/2 sanitary tee. The rest of the loop would be eliminated as would the Y below the tee.

    John
  8. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,060
    Location:
    Cave Creek, Arizona
    drain

    It is NOT an "S" trap because as long as the vertical pipe is NOT full of water it will have enough air in it to vent the trap through the inverted "U" fittings. Since that condition will occur when the sink is almost finished draining, AND that is also the time when a vent is needed to eliminate siphonage, it will perform its intended task most of the time.
  9. Redwood

    Redwood Master Plumber

    Messages:
    7,450
    Location:
    Connecticut
    BTW that old disposer is shot!
    I guarantee it!
    Look inside and I guarantee its toothless.
  10. stillad

    stillad New Member

    Messages:
    3
    Location:
    Huntsville, AL
    ...so use an AAV then?

    Thanks for all the helpful replies.

    With that said, it sounds like the consensus is that i can get rid of the screwy island loop as long as i install an AAV above the sanitary tee.

    Am i correct in thinking that?

    If so, does it matter how far above the sanitary tee i install the AAV?


    Also, what is that thing called that i have instead of an S-trap? Is it an O-trap? Maybe a P-trap? I'm not real familiar with the terminology...

    Do i need to replace it with an S-trap? Is it superior or inferior to an S-trap?

    Thanks.
  11. seaofnames

    seaofnames DIY Senior Member

    Messages:
    162
    Location:
    Mission, BC
    The use of an AAV depends on your local code allowing it. If it is allowed, it should be the last option, as it seems to be for yourself(since you want it easy).

    Remember that an AAV has moving parts and is will fail at one point.

    You dont want any other trap other than a P-trap. Everything else is either illegal and/or just doesnt look right(like what you have now).
  12. SewerRatz

    SewerRatz Illinois Licensed Plumber

    Messages:
    1,705
    Location:
    Chicago, IL
    Alabama approved AAV's. There are 15 states that do not approve the use of AAV's and there is 9 other states that approve them if you clear it with the local code officials.

    Also here is my favorite picture of the yoke vent.

    Attached Files:

  13. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,060
    Location:
    Cave Creek, Arizona
    trap

    You have a "P" trap connected to a bastardized version of a yoke/loop vent. It will perform better than an air admitance valve, and when drain system problems occur it will have the same problems as an AAV.
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