Sanitary Drainage
Sanitary Drainage tests whether you can size and slope drainage piping, select proper fittings, and provide cleanouts and maintenance access. The exam emphasizes drainage fixture units, slope by pipe size, and fittings that do not create a blockage or trap-seal problem.
Slope and sizing
Under IPC 704.1, pipe 2 1/2 inches and smaller slopes at 1/4 inch per foot, while 3-inch and larger pipe slopes at 1/8 inch per foot. Drainage fixture units from Table 702.1 are used with the building drain and branch tables. Slope must be uniform, and the pipe must be supported and aligned.
Fittings and direction changes
Vertical-to-horizontal drainage uses sanitary tees or approved fittings. Horizontal-to-horizontal changes and horizontal branches use wyes and combination wyes with bends. A sanitary tee should not be used where flow turns from horizontal to horizontal. Each fixture needs a trap, and the trap arm must be vented within the allowed length.
Cleanouts
Cleanouts are required at the base of each stack, on the building drain, at changes of direction greater than 45 degrees, and at intervals not exceeding 100 feet. They must remain accessible. Backwater valves are needed where the building drain can be flooded by the public sewer.
Worked example
A 4-inch building drain runs 60 feet at 1/8 inch per foot. The total fall is 60 × 0.125 = 7.5 inches. Using 1/4 inch per foot would produce 15 inches and would not match the required slope for 4-inch pipe under IPC 704.1.
Traps that cost marks
Using 1/4 inch per foot for 4-inch pipe is a common wrong answer. Another is placing a sanitary tee on a horizontal-to-horizontal turn or omitting a cleanout at the base of a stack.