Shower stall “pans” need to have a standard slope of 1/4-1/2″ per foot into the drain. Furthermore, they need to be made entirely waterproof, even if you are laying them on a slab. If you are making your own, as opposed to using a prefab pan, this usually involves laying down a lead or membrane barrier. You need to be especially careful about the joint between the barrier and the drain. The details are available on-line or in trade publications. These will also describe the proper DWV setup for your shower. It isn’t very complicated, but you’ve got to get everything right.
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