A 4 in building drain runs 96 ft from the last fixture connection to the point where it leaves the structure. Installed at the code minimum slope for its size, what is the total fall?

Explanation

Drainage pipe 3 in and larger may be sloped at a minimum of 1/8 in per ft, so 96 ft x 1/8 in = 12 in of fall. 6 in results from using 1/16 in per ft, which is allowed only for 8 in and larger pipe where approved, and 24 in comes from applying the 1/4 in per ft rate used for 2-1/2 in and smaller pipe.