First, you will need to know that ¼" per foot is the grade/slope/pitch/fall. Second, you need to know that invert means bottom of the pipe. The top of the pipe at the high point is 18", plus 2" for the pipe diameter, then add all the offsets 50’ + 40’ + 12’ + 75’ = 177’ 177’ ÷ 4 = 44 ¼" fall 18" + 2" + 44 ¼" = 64 ¼" From the finished floor to the top is 18" at the high end. The pipe size is 2" in "diameter". The pipe run drops 44 ¼". The 44 is inches as well.