Drainage Cleanout Layout (IPC 708)
Three triggers put cleanouts in a drain and they ADD, so counting from any one comes out low: spacing not more than 100 ft along the horizontal run, a cleanout at every change of horizontal direction over 45 degrees, and one at the base of every waste or soil stack. The allowance that keeps a bendy run sane is the grouping rule -- where more than one such change happens within 40 ft of developed length, the cleanout at the FIRST serves them all, which caps the change-driven count at ceil(run/40) however many bends are drawn. A 240 ft run with nine bends and two stacks needs 10, not 13, because the cap governs at six. Also checks access, which is where cleanouts get value-engineered into uselessness: 18 in of clear space at the opening for 6 in and smaller, and 24 in of unobstructed pathway height in a crawl space -- one you cannot reach and turn does not count.
Formula and source
spacing cleanouts = max(0, ceil(run / max spacing) - 1), assuming the run begins at one; change cleanouts = min(changes - grouped away, ceil(run / 40)); stack cleanouts = one per waste or soil stack; total = the sum of the three. Access passes when a cleanout 6 in and smaller has at least 18 in of clear space at the opening and, in a crawl space, at least 24 in of unobstructed pathway height.
IPC 708 - horizontal drains provided with cleanouts not more than 100 ft apart; a cleanout at each change of horizontal direction greater than 45 degrees, with the cleanout at the first change serving all changes occurring within 40 ft of developed length; a cleanout at the base of each waste or soil stack; not less than 18 in of clear space at the opening of cleanouts 6 in and smaller; and not less than 24 in of unobstructed pathway height where a cleanout is located in a crawl space.
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