Whirlpool tub/shower trap

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Gregg G

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Finished setting the 2nd bath whirlpool tub/shower yesterday in the new house. Followed Terry's advice re:several "piles" of mortar. On the first try some of the piles were too low. Pulled it out and added mortar
to all the piles without a "dent" and the second time it seemed to work like a champ. We put plastic between
the mortar and subfloor, and then another sheet between the piles and the tub. It was easy to pull the tub
out after the first try because of the plastic!

Anyway, the tub has a 1-1/2" tailpiece at the bottom of the overflow. I believe "only showers" need to have
a 2" trap, and "only tubs" need to have a 1-1/2" trap. For the "combo" tub/shower it looks to me like the
WA/UPC code only requires a 1-1/2" trap. Since the tailpiece is 1-1/2" I can easily use a 1-1/2 P-trap, or I could
put a 1-1/2 - 2" Fernco on and use a 2" P-trap. Or I could use a 1-1/2" P-trap and then increase to 2" pipe just
after the trap. The 3" toilet line is very close, so either way the tub will enter the 3" line within a few feet.

What is the recommended or more common way to plumb the tub? 1-1/2" P-trap or 2" P-trap? Do I even need
to increase the line to 2" since it's going to enter the 3" line so close? Of course, there will be a 1-1/2" vent on
the trap arm before entering the 3" line. New construction, so either way is just as easy.
 

Terry

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An 1-1/2" p-trap will be fine for the tub. The drain on a tub is pretty small anyway.
If you want to use a 2" p-trap, that would also be okay. The biggest problem on tubs is hair.
 

Gregg G

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An 1-1/2" p-trap will be fine for the tub. The drain on a tub is pretty small anyway.
If you want to use a 2" p-trap, that would also be okay. The biggest problem on tubs is hair.


Thanks, Terry. I'll just use the 1-1/2" P-Trap and then run the 1-1/2" line into a 3x3x1-1/2 Wye just downstream of the toilet.
I just need to make sure the 45 on the wye is clocked so it's above the midpoint of the 3" line, yes?
 
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