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Thread: Easy Question

  1. #1
    DIY Junior Member Hydro's Avatar
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    Default Easy Question

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    Hi, new to the forum with a quick question. I am changing from a double sink to a single sink on a bath/shower remodel. The new sink cabinet will be where the 2.5" vent is. The old sink drains are on the other side of studs. I crudely painted in how this all ties together behind the drywall with photoshop----the vent line goes up through the roof. This drain and vent piping tie in under the house to a 3" ABS waste line. My questions are:

    1. Can I just tee into the vent line for the new sink drain?

    2. If so, should I cap the old sink drain lines when I removed the peatraps, or put a coupling in and keep everything tied in?

    3. For the water, can I just plumb over from the adjacent copper piping rather tieing in directly below under the house. I have decent water pressure, and don't think I'd lose all that much adding the elbows in, but input welcome. If I'm running over from the old piping, it would probably be easier if the old drain lines were cut and capped and out of the way.

    Thanks,

    RICK
    Last edited by Hydro; 07-28-2011 at 03:09 PM.

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    From the way it is plumbed now, it looks like that vent line is the vent for fixtures below it. If so, you cannot use it as a drain. You should be able to cap one of them, and run the drain to the other (probably the one on the right), or run a new one down from that stud bay and vent it into the line coming up from below at 42" or 6" above the flood rim of the sink, whichever is higher.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    Test, Don't Guess! cacher_chick's Avatar
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    I've never seen a 2.5" ABS pipe, so if it IS, I doubt you could find the proper tee to connect to it.

  4. #4
    DIY Junior Member Hydro's Avatar
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    I'll check the size of that vent when I get home. Thanks for the feedback so far. Just to be clear, those pipes all tie into a 3" line just under the floor.....and they all tie in together where I have drawn in the piping just above the drywall cutline. Bear with me on this, but why is it a no go to tee off the vent for the new drain? If it is because if there is a blockage between that new tee and the waste line below, the vent would not work? If that's the reason (which makes sense) why couldn't the other two drain lines for the old sinks serve as vents if I cut out those tees and couple them back together.

    Just trying to understand the physics here. Re-routing the old drain on the right could be done of course, but then I'd have several horizontal feet for the water to flow, and I worry it wouldn't be very efficient (or worse). Installing another tee into the 3" line below the house and running a new drain in the new stud bay is not a great prospect if there is another good option, plus now that location is going to get a little more crowded sharing space with the existing vent pipe and the new copper piping. But I'll do it if that the right way to do it.

    edit: Further research on this forum revealed that no vent pipe should have horizontal runs at all. But is it that big a deal with what I'm considering?
    Last edited by Hydro; 07-28-2011 at 05:32 PM.

  5. #5
    Moderator & Master Plumber hj's Avatar
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    He is measuring the o.d. of the pipe and using 2" for 1 1/2" pipe and 2.5 for 2". I am having a hard time figuring out HOW you intend to revise the piping. I think you are giving us TOO MUCH information. ALL we need to know is EXACTLY where the new sink drain will be. Put a "dot" on the picture and we can tell you what to do. If it is where the "2.5" pipe is, rotate the tee on the left hand "2 inch" pipe and put an elbow next to the 2.5 pipe.
    Last edited by hj; 07-28-2011 at 06:14 PM.
    Licensed residential and commercial plumber

  6. #6
    DIY Junior Member Hydro's Avatar
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    Sorry, the old drains are 1.5", and what is labeled the vent is 2 inch. I sent the original post at work, and guessed wrong.

    Centerline on the new sink cabinet, which is 24" wide, lands a couple of inches to the right of the existing vent. That's right about where you can see the copper pipe that elbows through the wall there, which supplies a toilet in a bathroom on the other side of the wall.

    Thanks, HJ......but just to ask the original question again....is it a terrible idea to put a tee into the 2 vent line for this new sink drain or not?
    Last edited by Hydro; 07-29-2011 at 08:37 AM.

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