I have a Lasco one piece fiberglass shower stall.....its 32 or 36 inch..regular front walk in type. I need to know how to set this thing on a concrete slab type house. There was an old shower where I want to put it....but it was built crappy and it rotted some wood in back now I have to repair before the fiberglass unit goes in. I was planning using the old drain if I can chisel this old concrete up enough to splice in some new pvc for a stub for the Lasco unit. But what I need to know how do I drop this unit on the drain pipe stub or the fitting I need to do this without any leaks down the road. This has to be dropped down on the pipe drain right? Because there is no way to get under a concrete slap to do any pipe work underneath. Need some instruction...thanks. any photos also would be appeciated as this shower stall came with the worst instuctions I ever saw....does not even give a single instruction on concrete slabs.