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Thread: Sunday is "D(rain)-Day" -- and trap's offset is wrong.

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  1. #1
    DIY Senior Member miamicanes's Avatar
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    Default Sunday is "D(rain)-Day" -- and trap's offset is wrong.

    Well, the day I've simultaneously dreaded and anticipated has arrived (well, technically... I still have to go to bed and sleep before the big project in the afternoon). I'm stressing out badly, if only because this is one of the few tasks I can't do alone (at least, not without risking damage to the new tub), and tomorrow's the only day my friend can come over to help me until... well... about 2 weeks from now. So it has to be done tomorrow.

    The biggest problem I'm seeing right now is the apparent fact that the old bathtub's P-trap is about 3 inches too far back. If you look at picture 1, you can see how I calculated it:

    tub edge to back of overflow drain: ~5.75"
    overflow drain, front to back: 2.25"
    back of overflow drain to tub edge: 3.5"

    subtracting .75" (half the 1.5" pipe") from 5.75" suggests that the new overflow drain's pipe is going to be approximately 5" back from the stud. The old pipe was apparently ~2.25" back from the stud.

    Now, for the fun. As far as I can tell, I've removed everything from the old drain that can be nondestructively removed. It looks like everything from this point is going to involve cutting and gluing PVC.

    The fun part, of course, is the fact that the two vertical pipe sections are both inside the ~8" diameter hole formed in the second floor's slab (the bottom of the hole is the top of the living room's drywall), so getting a saw in there won't be fun, and would probably require buying some expensive new tool(s). HOWEVER, replacing the entire P-trap won't be much more fun, because it only has about an inch before it disappears into the slab.

    I should mention at this point that the bathroom is actually a slab cast on top of another slab. The builder formed the second floor's slab, then poured a second slab (delineated by the wood around the drain pit, and elsewhere around the bathroom's perimeter) with the drain pipes embedded inside. In a pinch, I could probably pry away the board the drainpipe passes through to get another half inch of pipe to work with, but for obvious reasons I'm nervous about cutting the pipe, because if I cut too much, the only way more pipe can be exposed is by breaking away concrete (at god knows what cost). The new 1x2 boards you see at the very top are coming off... I only needed THEM to dam off the area around the self-leveling concrete I poured yesterday.

    So... any suggestions for which pipe to cut tomorrow after I've confirmed that the trap needs to be shifted 2-3 inches further from the wall? Is there any easy way to cut a "pipe in a pit"? Or is my only real option to cut away the entire trap, preserving as much of the pipe sticking out of the slab as possible? What's the absolute minimum length I can have before I'll have to pry away the old board used to form the second slab to expose enough for a proper glued joint?

    By the same token, is there any good way to do the new trap in a way that will leave the door open to a third new drain, put in by me or whomever owns the house 25 years from now, without requiring slab breakage? Perhaps a PVC-to-[brass|galvanized steel|something-non-glued] fitting, so that going forward any new trap can be screwed on or compression-fitted instead of glued? That's my biggest objection to gluing a new trap into place... once the new trap is glued, there won't be enough exposed drainpipe left to ever cut THAT trap off and glue a new one to replace it.

    Alternatively, are there any good ways to "cheat" and somehow use another section of pipe between the old trap and new drainpipe's bottom to shift it ~3"? God forbid, maybe a flexible pipe kind of like the ones they sell to make connecting sink drains easier?
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  2. #2
    Journeyman/Inspector Inspektor Ludwig's Avatar
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    If it were me, I would cut the pipe just above the u bend in the trap leaving as much pipe as possible coming down from the 90 sticking out of the wall. I would go get a new trap and trap adapter and a 1' piece of PVC (bring the cut out u bend and trap adapter with you). I would also get what's called a "mission coupling". It's a rubber coupling with metal band around it and use that as the coupling between the pipe coming down from the 90 and the u bend. It tightens with 2 hose clamps and will allow you to move the trap left or right without having to worry about being permanent but you'll need to add a piece of pvc to outlet side of the new trap so the coupling has something to grab onto. Before you glue anything together dry fit everything because you may need to trim the pipe coming down from the 90 so the bottom of the trap will fit.

  3. #3
    DIY Member WorthFlorida's Avatar
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    The way it looks is the tub sits on top of the 2x's above the concrete floor and the pit was formed just for the trap. To get the few more inches you can chip away at the concrete. It is really not that hard. Sometimes a cold chisel will do or with a concrete bit drill holes next to one another then chip away at it.

    As far as the pipe is concern that is a bitch. You can cleanly cut the pipe right at the rim of the elbow to preserve as much pipe out of the floor as possible but here is the new problem. The pipe will be too short to glue on another elbow. The elbow will not reach the same spot in the pit. You cannot glue on a coupling becuase then it will extend to far over the pit to glue on a elbow. Using "street" elbows after the cut pipe might do the trick. Buy a bag of fitting and start playing around to see what might work. 45 degree couplings might work. I haven't looked it up but if 45 degree street elbows are available then that may work better for you.

    The finale way is cut the pipe and use those rubber couplings, (as stated above) with the two stainless steel clamps to extend the pipe after the cut to get the fit you need.
    Last edited by WorthFlorida; 11-22-2009 at 05:01 AM.

  4. #4
    Moderator & Master Plumber hj's Avatar
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    Default drain

    Well, if it were I, and I was REALLY concerned about that guy 25 years from now, I would "peel" that elbow off the pipe and start from there. BUT since I am not, I would cut the elbow off and not worry about the future.

  5. #5
    DIY Senior Member miamicanes's Avatar
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    OK, just to sanity-check... does everyone agree that the only purpose of the wood lining the perimeter of the upper slab was forming the concrete, it was just left in place because there was no particular reason to go to the trouble of removing it, and that my best option is probably to cut off the trap (leaving as much straight pipe between the first elbow and where the straight pipe emerges from the slab as possible), then remove the board if necessary to expose more pipe?

    As far as mission couplings go... I'm going to hit a few plumbing stores (I think there are a couple that are open until noon on Sunday). Are they really reliable enough to use in places that aren't easily accessible for future inspection? Or were they mainly designed for places that are semi-accessible, like basements and crawlspaces, so you can see if the connection is failing and fix it before it becomes a major problem? When you say "rubber", are they REALLY rubber, or are they actually some other material that won't crack, shrink, harden, etc over time?

    Finally, is it safe to assume that Sharkbite-type couplings for 1.5" PVC pipe don't exist? ;-)

  6. #6
    DIY Member WorthFlorida's Avatar
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    This is the link to "Mission Rubber Products" Their stuff is pretty good and it may take 25 years to leak. as long their is no electric motor nearby (ozone generator).If this type of joint every leaked it would only drip straight down in that 8" pit and the water would show up on the ceiling below, This is what you want. The future owner will see a wet spot, open the ceiling and will be able to replace the joint and fix up the ceiling. A real easy fix.


    http://www.missionrubber.com/Product...lCouplings.php
    Last edited by WorthFlorida; 11-22-2009 at 10:15 AM.

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