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Thread: Sink Drain

  1. #1

    Question Sink Drain

    I'm adding a new sink to a basement bathroom. When the builder stubbed off for a sink drain, he mounted it a little low. So I want to do a 90 up and a 90 out to better line up with the sink drain (and to bring the 'p' trap off the bottom of the cabinet).

    I hope this diagram helps



    As you can see the pipe is 1 1/2" ABS.

    So is what I want to do OK, or will it cause poor drainage from the sink?!

    Thanks for the help

    Sean

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    I think you can do that, but you don't indicate a vent...that would normally be going up from where it goes in the wall. How far away is the nearest vent?
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    Commercial Plumber markts30's Avatar
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    I am assuming the original roughin had a vent...
    You cannot go up with the 90 like that - that is an STrap...
    Best bet would be to go to the original santee with the vent... cut it out of the pipe and splice it back in 6 or so inches higher with some banded couplings....
    That will give you the height you want without the STrap issue...

    On the other hand, if the drain the sink comes off has waste from the upper floor(s) in it, you cannot use it to vent the sink and will have to take the drain line, sweep up into a san tee for the trap arm of the sink, then run a vent to the nearest vent (not drain) and tie it back in...
    Make sure this tie in is at least 6" above the flood rim of any fixture the vent serves.
    Last edited by markts30; 08-08-2007 at 02:39 PM.

  4. #4
    Homeowner geniescience's Avatar
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    both posts above discuss things happening off the far right hand side of your diagram. Without knowing what you have over there, it's all just speculation. Can you draw that in too? You are good at drawing.

    David

  5. #5

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    Here's a drawing with more info.


    Hope this helps!!

    Thanks guys

    Sean

  6. #6
    Homeowner geniescience's Avatar
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    what happens between the far right hand side and the P trap? Nothing? Straight pipe? Only a P trap there? No other pipe visible? No vent coming down from above? No Tee? No Wye?

    Or, is there a vent pipe (i.e. vertical) and a connection point, which the P trap runs into?

    If not, then no you probably won't get anyone's blessing to run the drain as shown, since it drops before being vented. Several ways to work around this problem, if this is what it is.

    David

  7. #7

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    Sorry about that!!

    It just come out of the wall and into the 'P' trap



    Sean

  8. #8
    Licensed Grump GrumpyPlumber's Avatar
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    Just to restate what Markst said...maybe simpler...
    Any time you drop a drain more than 45 degree's you need a seperate vent because the momentum tends to siphon the trap...emptying a full basin of water would likely suck all the water from the trap.
    "The biggest regrets we have in life are the chances we never took."

  9. #9

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    So would it be better if I used a 45 instead of a 90. Right now the wall is closed up, so getting to the main drain/vent would mean tearing the wall up, and I'm hoping to avoid that. I left a 12" opening in the drywall to attach this drain.

  10. #10

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    The picture I show is how it is. The main 2" line to the left is where the venting is. Everything after the 1 1/2" stub is what I want to do.
    What it sounds like is that I can't drain a sink with two 90s. I'd have to ADD another vent above the stub out for this bathroom sink to drain.
    I just don't see venting like that in the walls behind the sinks in other parts of the house. The simply enter the wall and drop into a main line along the floor, to where the main sewer stack is, and the vent is on the back end of the run.

  11. #11

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    Quote Originally Posted by GrumpyPlumber
    Just to restate what Markst said...maybe simpler...
    Any time you drop a drain more than 45 degree's you need a seperate vent because the momentum tends to siphon the trap...emptying a full basin of water would likely suck all the water from the trap.
    I would think it would only siphon if the pipe ran at full capacity. I don't think there would ever be enough water in the drain to completely fill the pipe.

  12. #12
    DIY Senior Member Jeff1's Avatar
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    Default Just wondering

    Couldn't you just use a longer pipe coming out of the drain?

  13. #13

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    Here's a picture of the situation prior to copper and drywall. So the room is completed with an access hole where the stub out is.



    So at the end of the stub I wan to add an 90 up and a 90 out to get it up and in the previous drawings. (That stub is about 20" off the floor)

    Sean
    Last edited by MaximAvs; 08-09-2007 at 12:33 PM.

  14. #14

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    Quote Originally Posted by Jeff1
    Couldn't you just use a longer pipe coming out of the drain?
    I did look at that, but then the P-trap is really close to the floor of the vanity.

  15. #15
    Forum Admin, Expert Plumber Terry's Avatar
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    Cut out the tee, and raise the trap arm pipe.

    Or, use a longer tailpiece going into the top of the p-trap.

    If you use fittings to raise the pipe before the p-trap, you create an S trap that will siphon the p-trap.

    If you siphon the p-trap, your wife will be complaining that the bathroom smells.
    Do you really want that?

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