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Thread: trap design help on new vanity

  1. #1
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    Default trap design help on new vanity

    Hi all - been lurking for a bit (great, informative site!!) and haven't found a clear answer on what I'm looking to do. I'm at the final stages of a bathroom remodel and am at the point of installing new vanities. I'm putting in 2 separate 24" vanities to replace a 78" dual sink vanity.

    My problem is where the drain line comes out of the wall and lining it up with the sink and trap. The shelf of the vanity is directly in line with the drain line. I've already got the walls back together, so moving the drain isn't really an option and I realize I'll be cutting into the back of the shelf (no big deal, as the doors will hide most of it).

    My question is in regards to the design of the trap. I know that it's desirable to have the trap right below the sink. But, is it OK to have a 45 or 90 angle under the sink and then have PVC go back towards the wall then another angle to drop it down to the level of the drain line (it's only about a 15" drop from the bottom of the sink to the drain line)? I would then put the trap right before the drain line. From reading hear, it sounds like this would better than putting the trap right under the sink and then dropping the line down to the drain line level.

    The intent is to move the trap back closer to the wall to minimize the cutting of the shelf. This would be similar to what you might see in wall mount designs, where you don't want to see all the pipes right under the sink, so you have a horizontal pipe (pitched, of course) back to the wall and out of the way.

    Does my description make sense and is this something that will work without affecting the flow of the drain? Any input is appreciated. Thanks

  2. #2
    Forum Admin, Expert Plumber Terry's Avatar
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    The trap arm is level with some down grade, 2% toward the vent.
    With a 1.5" line, you can go up to 42"

    Dropping the trap arm creates an S trap will siphon.


  3. #3
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    OK - so I'll put the trap immediately before the drain line at the same level (2% downgrade). But can you have angles between the trap and the sink drain?

  4. #4
    Forum Admin, Expert Plumber Terry's Avatar
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    Can you have angles between the trap and the sink drain?
    They make offset tail piece drains that 90 over closer to the wall.
    Yes, you can use fittings to drain into the p-trap.

  5. #5
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    Great - thanks for the clarification.
    And thanks for the great forum. Between you and John Bridges Tile World, I've learned a ton and saved thousands of $$$!

  6. #6
    Moderator & Master Plumber hj's Avatar
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    Default drain

    Two things to consider;
    1. making the offset will create a very unstable drain because of the multiple joints and it can start leaking if it is bumped frequentlu.
    2. The typical pop-up drain may be too long to allow you to make the offset to the trap, given the space that the offset fittings will require.

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