I had a plumber rough in for a bathtub installation on a slab. He left a 12" x 12" hole in the concrete for access to the drain stub. Now what? I know you shouldn't fill it back in with dirt and I need to create a pit, but how? With what? I read somewhere that people line the dirt with tar but that does not seem very practical, polished, or professional for a finish.

Is it possible to make a concrete box at this point? Should have this been created before the concrete was poured to begin with?

Should the P-trap be all socket welded and covered up with a threaded connection for the bathtub drain and cemented in leaving enough clearance to remove the drain? That approach seems very unforgiving.

I have the hole, so now what do I do with it?

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Originally Posted by mnbob

I had a plumber rough in for a bathtub installation on a slab. He left a 12" x 12" hole in the concrete for access to the drain stub. Now what? I know you shouldn't fill it back in with dirt and I need to create a pit, but how? With what? I read somewhere that people line the dirt with tar but that does not seem very practical, polished, or professional for a finish.

Is it possible to make a concrete box at this point? Should have this been created before the concrete was poured to begin with?

Should the P-trap be all socket welded and covered up with a threaded connection for the bathtub drain and cemented in leaving enough clearance to remove the drain? That approach seems very unforgiving.

I have the hole, so now what do I do with it?

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You're worried about the Tub dap-out? What is it that disturbs you? We do not fill, line or encase a dap-out unless the contract calls for us to do so, and then we just pour melted tar on the top of the dirt. What "polishes finish"? For a dap-ouyt? Your "P" trap and raiser is positioned to pick up the tub and is glued in place to make a perminate installation. . In short I believe your fears are groundless. Ya want to know whot comes next? Ya connect a bathtub over the dap-out and forget it. This is a after thought. Have I made a mistake in assuming that, just because we always install a trap and raiser in a tub dap-out that you have one installed?
Good luck, Tom

Mnbob... are you planning to install a tub now... in the future? Sounds like you have what they call a tub DAPOUT... now there may or may not be wood in box... could have been pulled out... what matters is that you have a 12" x 12" box in the concrete.

Inside that box is a pipe that will need to hook to a ptrap (I use the socket weld ptrap with full size union cleanout... see 1st pic. Below) and then to a tub waste and overflow assembly with a tailpiece that will connect into the ptrap via an 1.5" PVC desanco fitting (see 2nd pic. Below.. it is brass... but you get the idea).

If you will be setting a tub you will need measurements to center drain before beginning to try to hook up drain... Note here that center of drain right to left is determined by your tub drain (usually between 14 and 16 inches to center of rough stud wall)... the center of drain front to back is determined by the tub waste and overflow assembly(see pic.3 below) you attach to tub (this front to back measurement is usually 1.5 inches to center off the end of the rough stud wall).

Anyway, once you have those measurements, you will DRY FIT the ptrap to where you think it will go... THEN you will remove the ptrap... lower tub in place... and THEN dry fit the ptrap again.. if all looks good then you will prime/cement all together and test the drain and overflow assembly (fill tub to past the overflow assembly and drain).

Point of all this is that you will need to access this drain piping after you install the tub.

So there... that is what you do with a tub dapout.

BUT if you are not setting a tub...then just leave it alone...someone may want to set tub in future!!

Hey, hope that answers questions. Good luck... let us know what you end up doing. You can RATE THIS ANSWER if you like. Thank you