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Thread: 45's to raise p-trap arm?

  1. #1

    Default 45's to raise p-trap arm?

    New vanity in a bathroom remodel has a cabinet floor that is several inches higher than the old vanity floor. It comes to just below the bottom of the drain outlet coming from the wall. Just enough room to run the horizontal trap arm and tighten the slip joint. The DWV is in the wall just beyond that. The DWV looks like 2" or more, the tee is 1 1/2, the trap arm fits into a 1 1/2 x 1 1/4 adapter.

    To install the p-trap from the lav drain normally, I'll have to really hack out the bottom of the vanity to accomodate the bottom of the p-trap before connecting it to the trap arm.

    Is there some other solution? Is it OK to use 1 1/4" 45's in the cabinet to raise the trap arm enough to allow the p-trap to fit without cutting into the cabinet base? Any other ideas that will help without forcing me to cut the new vanity base?

    Thanks...

  2. #2
    Master Plumber Redwood's Avatar
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    That would create an unvented s-trap.
    The right way would be to raise it in the wall.

  3. #3

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    Quote Originally Posted by Redwood View Post
    That would create an unvented s-trap.
    The right way would be to raise it in the wall.
    In this case, raising the drain tee in the wall is not the best solution for me. The walls are newly tiled wainscot. Cutting into it would be too tricky for me; and the other side of the wall doesn't have decent access to the DWV line

    From what you say, I'm guessing that /any/ downslope on the horiz trap arm would also be a form of s-trap? Is there a minimum length for the trap arm? If not, would it be OK to put the p-trap and [a very short] arm within an inch or so of the drain inlet?

    That way I could locate the cut for the bottom/bend of the p-trap near the back edge of the cabinet and run 2-45's from the tailpiece of the lav for some drain slope to the top of the p-trap (or simply 2-90's?). In this method, the "horizontal" trap arm would be just a short connector to the tee, and no s-trap is formed.

    If this isn't workable either, then I don't see any choice but to cut the vanity floor near the center and hope for a neat/trim fit. No fun here today

    Thanks...

  4. #4

    Smile this may work?

    What type of tee is in the wall? If you can adapt to that, possibly with a 1.5 " female adapter, come out of the wall and 90 up. Put another sanitary tee vertically, come out of the top with an air admittance valve. Now retrap the lav as you would normally.

  5. #5
    Master Plumber Redwood's Avatar
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    Take a look into the connection in the wall.
    Is it an elbow that goes right and left, or is it a tee with a vertical pipe behind it?

    It would have been nice to get this right before the new wall.

    If the pipe is vertical any repair could be hidden by the vanity.

  6. #6

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    How high does the AAD have to be? There isn't much height under the lav. The center line of the drain to bottom of lav is about 21".

  7. #7

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    Hi Redwood. Yup you're right on that, should've fixed it properly before the tile guy did the wainscot wall. Poor planning, I didn't count on the new vanity floor being that much higher than the old one <grrr....>. Figured new vanity going where the old one was so I'd be OK. Anyway:

    I've found some pics of the other side of the wall near this drain outlet, and the drain line to this lav seems to be a short (about 12"-16"") 1-1/2" pvc horiz run to an elbow out to the lav. I say "seems to be" because all I can see is the DWV tee and the start of the horiz run towards this lav drain.

    So I was incorrect in my first post: the lav drain does not directly connect to the DWV line with a tee out. It is an elbow off a horiz run from the tee out of the DWV. Is there any way to fix this without going back to the tee and raising the tee? Even if I break into the tile behind the lav I won't be at the tee. I can't get at the tee without really messing up the wainscot'd wall outside the vanity to where the DWV stack would be.

    Seems anyt upslope I do that is upstream of the tee and downstream of the p-trap would effectively create an s-trap? If that is true it comes down to minimizing the cutting damage to the vanity floor. Can I do what I asked about before: notch out the back of the vanity floor to accomodate the p-trap at the wall-out, 2-45's to get to the tailpiece? Is that a workable and would it be effective?

    Thanks for helping...

  8. #8

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    OK, found the picture of the other side of the lav wall I'm working on. The view here is the bathroom lav plumbing on that other side, the first bathroom that was remodeled 3 months ago. The bottom tee going out to the right is the horiz line that connects to an elbow that goes through the wall to the lav drain I'm working on. Confusing?
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  9. #9
    Retired Defense Industry Engineer jadnashua's Avatar
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    If you cut that horizontal run and replace with a couple of 45's in it, you could raise it.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  10. #10

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    Jim, that was close to what I was first asking: putting a pair of 45's at the outlet coming out of the wall, upstream of the elbow, downstream of the p-trap.

    Redwood responds that 45's downstream of the p-trap, before the tee, effectively create an s-trap, that I would have to raise the tee. Are you saying that the 45's would be OK? Even more confused

    Thanks...

  11. #11
    Master Plumber Redwood's Avatar
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    Maybe this picture will allow you to grasp the concept of the venting on a dirty arm like that. While the picture shows a correctly vented dirty arm on the left with a sani tee, on the right using a combo or wye and street 45 creates the s-trap effect. See how the flow of air along the top of the pipe is cut off when you drop too far. Using a couple of 45's will do that.


  12. #12

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    vistaman if you 45 that lav arm at all , you will cut off the vent. what i said before will work fine, 90 right out of the wall and put a sanitary tee on the 90. The AAV needs to be only 4" above the top of the trap (maybe more depends on the manufacturer of the valve) so if you have 21" of play you should have plenty of space.

    This is the only way to do it legally, however if you are not being inspected, go ahead and 45 up. It will still drain fine.

  13. #13

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    Thanks for the drawing Redwood. I see how the syphon effect would work on that setup. But what about 45's /before/ the p-trap? Out of the tailpiece to a pair of 45's then down into the p-trap, and level/horiz out to the elbow? Would that be a proper method?

    There is also the alternative that NHJeremy proposes which apparently will work.

  14. #14

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    vistaman if you 45 that lav arm at all , you will cut off the vent. what i said before will work fine, 90 right out of the wall and put a sanitary tee on the 90. The AAV needs to be only 4" above the top of the trap (maybe more depends on the manufacturer of the valve) so if you have 21" of play you should have plenty of space.

    This is the only way to do it legally, however if you are not being inspected, go ahead and 45 up. It will still drain fine.
    That's some good info and it sounds like a workable solution. I don't have to worry about inspection here, but I do want a reliable drain that won't suck the trap dry

    Are san-tees and aav's available in 1-1/4" sizes? The 1-1/2" drain out has already been fitted (by tile guy w/the red-stuff glue) with a 1-1/2 to 1-1/4 reducing fitting for the trap arm.

    Thanks for participating.

  15. #15
    Moderator & Master Plumber hj's Avatar
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    You CANNOT use 45's ANYWHERE in the drain line before the vent connection. Your problem is that the original installer did not know how to install connections for two sinks back to back and therefore made one, the one you are working on, lower than the other side. IF he had been a good plumber the drains on both sides would be the same height and you would not have this problem. It could have been fixed when the wall was able to be opened. Now your best option is to cut a neat oval in the cabinet floor so the P trap can hang into it. OR maybe two circles with the P trap coming up from below.

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