Hi. I am in zone 4a. I am pouring a slab and have installed my subslab sewage pipe for a bathroom with 3×5 shower, washer, and mop sink. I have two questions:

1. Do I need to anchor the vertical pipes somehow so they do not budge and land in the 2×6 wall framing? I would just do that, yet i thought perhaps rebar next to schedule 40 PVC might be a bad thing?

2. Since I am installing a sub slab p-trap for the 3×5 shower, do I need to do one of those 12×12 boxes around the shower drain? I will be filling that area in anyways to build up a sloped shower base for the liner and tile. So, why not just eliminate that box and void?

I appreciate any clarification you can offer.

-Mike