calibrating a bath tub P-trap set in concrete

amakarevic

okay, so here is another conundrum:

i left an 8x12-in rectangular opening in concrete under where the bath tub drain hole is supposed to be. the 1.5-in pipe ends about a foot below the surface in the middle of the hole, i.e. is ready to get a P-trap attached to it.

once i set the framing around the supposed tub so that i can fit the tub, is there a trick to how to calibrate the P-trap, i.e. adjust the length of the protruding pipe. seems to me like it would be simply trial and error but was wondering if you all pros would know of a quicker and preciser way ?

thanks,

- a -

troubleseeker

That's about it, just dry fit together and cut lengths as needed. Put registration marks, a line with a Sharpie or such, on both pieces of fittings that have to be glued at a rotated position.

amakarevic

that was fast

jpplumber

The p-trap should be on the other end of that pipe lower in the ground as the p-trap has a vertical pipe coming in and a horizontal pipe coming out. In other words the p-trap should be on before you pour concrete.

troubleseeker

That is true. I assummed that he was referring to making up the drain/overflow assembly to the stub up, since he has an existing slab.

amakarevic

you are not understanding me.

how can i have the p-trap on before i know EXACTLY where the tub will be ? and i cannot do that before the concrete is ready and the framing has been set up.

a book that i have suggests that, when pouring concrete, i leave an 8x12 opening in concrete right below the tub drain hole. that is what i did. the PVC DWV pipe penetrates within that rectangle (horizontal, of course) about a foot below the concrete surface, i.e. is ready to have a p-trap mounted on exactly as you are describing. the pipe portion penetrating into the rectagular frame by about 3-4 in. i may need to cut off 2-3 in depending on the EXACT position of the tub.

make sense ??

Ron The Plumber

Measure to center of tub drain, that is center from the side wall, now 99% of the time the trap will line up on the very edge of the inside wall, then make up the drain for the tub once you get lined up.

If you have to offset to the tub drain tee or down to the trap, it's ok to do an offset.

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jpplumber

Sorry I misunderstood. You are right, I thought the pipe was coming up vertically, and the p- trap on the bottom of the vertical pipe, but yours sounds like it is going horizontal to a sanitary tee that probably has a vent. So just figure out where the waste and overflow drain will end up before you cut the horizontal pipe and glue the p-trap. You will be able to swing the p-trap (where the street 90 connects to the "u" portion of the trap) to find the right spot before you glue it all up.