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Thread: Possible sink vent?

  1. #1
    DIY Junior Member Randmness's Avatar
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    Default Possible sink vent?

    Hello,
    We are in the process of replacing our kitchen cabinets and sink in our condo unit, and came across the long PVC pipe that runs horizontally below the countertop and connect with the sink drain. In order to fit in the new sink, we need to lower this a few inches. I was a little apprehensive about touching this pipe, as I thought it might contain drainage from the unit above me. After looking around on this forum and others (I'm not a plumber by any means and I apologize if this is the incorrect forum), it looks like this may be the vent (about 40" from the sink) for the kitchen sink. Am I correct?

    Thanks.
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    Last edited by Randmness; 08-24-2012 at 09:17 AM.

  2. #2
    DIY Junior Member hagakure's Avatar
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    It's most likely a vent. I don't think a condo complex would have plumbers stupid enough to run a drain pipe from the floor above directly into the sink drain of the kitchen below. They would be draining into the same drain stack. I don't see how it could have passed inspection if that wasn't the case.

    Hopefully...

  3. #3
    In the Trades Gary Swart's Avatar
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    I do find it interesting that the dishwasher has its own P trap rather than the normal connection. As a DIY I can't comment on its legality, it looks like it should be OK, just strange. Usually the DW drains into the disposal or a special tail piece. What you have seems to me to waste a lot of under sink space.
    Last edited by Gary Swart; 08-24-2012 at 12:22 PM.

  4. #4
    DIY Junior Member Randmness's Avatar
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    Thanks for the comments. Knowing that its a vent definitely makes me less apprehensive about slightly adjusting its location.

    In regards to the DW trap, I will have to look up the local code for MD (Columbia), to see what it says regarding air traps. I would love to get rid of that trap and connect it straight to the disposal.

  5. #5
    Plumber jimbo's Avatar
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    Assuming it is a vent, it probably functions OK, it sort of meets the "spirit" of the code, but definitely does not actually comply with code. A vent cannot be horizontal ( less than 45 angle) when it less than 6" ABOVE the top of the sink. Keep this in mind if you want to change it.

  6. #6
    DIY Junior Member Randmness's Avatar
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    Awesome. When you refer to the vent not being less than 6" above the top of sink, do you mean 'less than 6" from the top of the sink'? The vent is a few inches (about 3 or so) below the counter top.

    I also had a few quick questions:
    1. When lowering the vent, is it recommended to slope the pipe down to the drain vs two 90 degree bends? I imagine the sloping (leveraging two 45 degree adapters) is better than 90 degree turns.
    2. Is it ok to run the pvc pipe behind the metal water supply pipes? However, the wall behind the sink is a cylinder-block wall (maybe 2in deep) so I wouldn't be able to completely hide the PVC in the wall. I will double-check the clearance when I get home.

    Thanks again.
    Last edited by Randmness; 08-24-2012 at 02:25 PM.

  7. #7
    Nuclear Engineer nukeman's Avatar
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    No. jimbo means that the vent shouldn't go horizontal until it is at least 6" above the top of the sink. Normally, all of this venting is done inside the wall. What you have isn't really legal, but it probably works fine. It appears to me that perhaps that sink used to have an S-trap at some point and then was converted to a P-trap (with the "vent") during the last remodel. To make it right, you would have to open walls and run the vent up the wall, but that can be difficult to do in a condo.

  8. #8
    In the Trades Gary Swart's Avatar
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    I believe the gentleman misunderstood my comment regarding his unusual plumbing. I was not referring to the air gap. Air gaps are required in many places. Some places allow a high loop instead, but this is not the basis of my comments. Your DW is going into a P trap and then into the sink/disposer drain which also has a P trap. The conventional way to connect a DW drain (after the air gap) is into the disposal. If no disposal is used, then there is a tailpiece that goes in the sink drain before the P trap that the DW drain hose connects to. Again, this is totally unrelated to the air gap.

  9. #9
    DIY Junior Member Randmness's Avatar
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    Thanks again for the responses. It looks like I am going to look into getting a plumber anyhow. The faucet is soldered on, and this quickly approaching the limit of a DIYer like myself. Hopefully, I can get all this PVC resolved. Now time to find a reputable plumber...

    I really do appreciate the help.
    Last edited by Randmness; 08-25-2012 at 12:09 PM.

  10. #10
    Plumber Winslow's Avatar
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    the horizontal PVC pipe is the vent for the kitchen sink, you can lower as necessary but you should try ond keep the offset above the drainboard (bottom) of the sink. As far as the dishwasher connection is concerned it is most likely illegal because you have 2 traps on 1 trap arm.That's illegal according to the UPC, not sure which code your jurisdiction uses.

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