Bathtub (with shower) trap size

[Paul Reece]

I recognize and understand the need for a 2" drain pipe from the tub to the stack, and I get it about vent location. But of course the tub drain is 1.5".
I had planned to transition immediately out of that 1.5" tailpiece into a 2" trap, but life would be so much easier if I could do the transition immediately out of the trap and into the drain pipe.
1.) Is this alternative just as good?... or even acceptable?
2.) Does the smaller trap shorten my vent arm?

The trap installation (and any later service) is fully accessible from the full basement below.
3.) If it IS okay to use the 1.5" trap in this run, then rather than a solvent weld trap, would a compression fitting installation make more sense for ease of servicing in the future?

If the 2" trap is in fact the required design,
4.) should I be able to find a 2" trap adapter with a compression fitting to accept the 1.5" tailpiece from the tub?

 

[hj]

1. Acceptable, but not as good in my estimation
2. No.
3. I prefer a solvent weld, because everytime you work on a compression trap, you run the risk of it breaking or leaking.
4. That is the way I do it.

 

[Sponsor]

 

[Paul Reece]

1. Acceptable, but not as good in my estimation
2. No.
3. I prefer a solvent weld, because everytime you work on a compression trap, you run the risk of it breaking or leaking.
4. That is the way I do it.

Thanks, HJ.
I'll go with the 2", solvent weld trap.
I can't find an appropriate 2 x 1- 1/2 trap adapter, so I'll just cement in a pipe "increaser" between the tub drain and the trap.

 

[hj]

You use a 2 z 1 1/2" bushing and a spigot/street trap adapter with a slip nut.