I have a 2" pvc straight running to the stack. Pipe was connected to trap in fiberglass kit. Now, laying tile on floor using concrete slab. Pipe was level. With kit removed, trap is now lower, causing pressure on pipe. Is it possible to install two 45's top and bottom, to ease pressure on pipe? Will shower have slow draining. Most important ! I have NO access to stack, or I would lower the pipe.

Installing 45's will kill the slope. What are you putting there now ? Tub ? Shower ? Plastic Enclosure ? Or Custom Built ? Please, give us more details. There is a solution to every problem but we must know what we are dealing with. Also, if you can, post photos. Back to you. Milo