how to rough in bathtub drain
Bathtub drain rough-in. The standard bathtub/shower combination will require an 1-1/2 drain and p-trap installed to your local plumbing code. The drain must be graded(sloped) at a minimum of 1/4 per foot and must be vented. This can be done in one of two ways, by wet venting the trap arm fixture drain or by individually venting the bathtub.