Laundry/Utility sink drain size.

In the midst of a rehab of our laundry room. Picked lots of good info about venting here -thanks, Terry for the standpipe/sink picture! (lots of sweated joints- I learned about taking your tme, cleaning the fittings, ..., after redoing it several times - but passed an air test yesterday.)

In CA, under UPC, need 2" drain for a laundry tub. Ok, put a 2" drainpipe in the wall. But most of the drain assemblies I see have a 1.5" tailpiece, which one would presumably feed into a 1.5" ptrap - does this comply , ie is the 2" req. only for the pipes in the wall?

Thanks!
Murray

A laundry tray uses a 1-1/2" p-trap and arm, into a 2" waste line in the wall. A 1-1/2" vent is fine.

The washer uses a 2" p-trap and standpipe.

Thanks Terry! I really appreciate your running of this forum. You and the other participants provide great advice and perspective.