I am installing two drains into a 3" stack that is outside my house. The first is a shower drain with 2" ABS, the second drain is the tub with 1.5" ABS. The tub drain is about 6 feet from the stack, while the shower is about 10 ft. My question, what is the reccomended grade for these types of drains? I have heard that 1/4" rise per foot run... but that seems pretty steep, and will mean I will lose more ceiling height. Please help, want to get the drains completed soon. Mike