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Question DetailsAsked on 1/31/2015

From shower to bathtub, mismatched drain alignment in concrete slab foundation

I am replacing my shower with a tub and the drain for where the shower was is in the center, but the tub is at the end of the tub. So I need to figure out a way to connect the tub drain which is a couple feet from the sewer drain which is in the middle of the shower area. The foundation is concrete. I can't find a pipe that will fit under the tub to connect that way, so I either have to raise up the tub or cut through the concrete to make a pipe connect the tub drain to the sewer drain where the shower drained. Any suggestions?

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1 Answer


Even if you found a pipe that would fit from the tub outlet to the existing drain in the floor, it would have no drop as it usually would before it went horizontal so would drain drain slowly. I would guess in shower mode (assuming this will be a shower/tub), the water would back up when you shower, like taking a shower in a kiddy pool. And of course, because it would be flowing slowly, any cracks or bad joints in the sewer pipe which might normally not leak in a normal downward configuration might leak under the tub, and will clog up easier too.

Also,, with a normal tub, you do not have room to put a trap in there between a tub and a concrete slab, which you definitely need. And using the shower trap would be a BIG mistake - no way to reasonably clean it, and going around two 90's to get to it with a snake - I just would not do it.

My recommendation - do it the normal way - cut through the slab, reroute the drain pipe to the correct location, correctly bed the new pipe in sand (do NOT concrete it in), and then repair the concrete.

Raising up the tub is probably not a great idea - first, unless you used concrete to raise it you run the risk of rot if there is ever any water under there (and with a tub there is commonly some condensation under it at times when over a concrete slab), and tubs are a problem for a lot of people to step into at older age (or for little kids) anyway, so raising it could affect resale value, especially if not done professionally on a formal raised dais like with a soaker tub - which takes and extra foot or two of bathroom floor space for the platform/steps.

If you do go with the raised platform, use concrete (leaving access to the pipes) or at least full ground contact treated timber that is recoated and let dry before installation.

Als, on the piping - I would not go from the existing drain/trap. I would intercept the pipe somewhere closer to the new drain if possible and cut into it there (preferably directly under the tub drain if possible), to minimize the number of turns you are going through.

You can find links to a couple of similar situation questions with responses below this answer, too.

Answered 5 years ago by LCD

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