I am installing a freestanding tub. There is fairly easy access to the rough plumbing in the basement. There is an integral overflow designed into the tub so there is only one tailpiece to deal with. The manufacturer shows using a trap flush against the tub then a flexible piece that connects to a floor drain.



I was thinking to just run a longer tailpiece down through the floor to a trap under the floor. There is a 3 inch drain pipe running almost directly underneath. I would then tie in the trap to the 3 inch drain pipe using a 90 sweep elbow into a sanitary tee. Is there any problem with this? I am preparing to lay the tile and I think I just need a hole big enough to fit the tailpiece through, but I will oversize it to make it easier since it will require lowering the tub down over the hole with the tailpiece pre-installed. If there anything wrong with this plan, please comment. Thanks.





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Cant use a sanitary tee on its back. You must use a wye and 45 or a combo with a 90. You need a vent before it goes vertical after the trap and can t use 2 traps.



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pretend this sink is the tub.
extend the tub tailpiece so you can have a configuration like this.
keep the top of the trap outlet pipe even with the bottom of the joist.
come out of the bottom of the san tee and run a 90 into a Y in your 3 inch.

OS&B makes a island tub drain specifically for your purpose. It uses your idea of the tailpiece and goes straight down through the drain membrane. I certainly would not the corrugated drain pipe.

[osb.ca]

Thank you for the responses. So I use a sanitary tee with an AAV combined with the circled parts in this photo to tie into the existing 3" line. Substituting a 3 x 1.5 wye for the 2" in the image:



Regarding the OS&B fitting. I have looked at those. I am having trouble seeing any advantage when I have access in the basement, and they are not cheap. Am I missing something?