A 4 in horizontal building drain runs 340 ft under a warehouse slab. Not counting the cleanout at the upstream end of the run, what is the minimum number of additional cleanouts required for spacing alone?

Explanation

Horizontal drainage lines 4 in and smaller require a cleanout at intervals not exceeding 100 ft, so a 340 ft run needs cleanouts at roughly 100, 200, 300 ft and at the far end, which is 3 additional cleanouts beyond the upstream one to keep every interval at or under 100 ft. Two cleanouts would leave intervals longer than 100 ft, while 4 and 6 exceed the minimum the spacing rule requires.