I have a Japanese tub I'm trying to get put in. One plumber told me there's no way to connect to the drain, so the only option is to put it inside a shower pan. But I'd really rather not do that.
The drain is made of plastic, has a threaded down tube with OD of 1.5 inches (measured with calipers).
What would you do? Tub looks a lot like this one
[ecx.images-amazon.com]
A regular tub would be too big to fit in this bathroom.



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What do you mean by "threaded down tube"? Is the whole thing threaded or just the top with the bottom section smooth?

I think the pipe could be adapted to, whether by solvent weld, threaded connection, or mechanical connection ( shielded coupling) .

@hj: The whole down tube is threaded on the outside. It's not very long, a couple inches.

I looked at shielded couplings, but the smallest rubber coupling I could find
is 1 1/4 " nominal, which is actually about 1.66" ID.



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Looking through a parts bin there are plastic sink drain plumbing kits that can
accept a 1.5 inch tail piece. Some even use rubber gaskets. If I can just fill
in the threads with putty or silicone it seems like a viable option? What would you
use?

Mission Rubber makes a shielded coupling for 1½" tubular to 1½" IPS(T150) or 2" IPS(T215). You might need to silicone caulk the threads, to get the coupling to seal better.



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