Sanitary Drainage, Storm Drainage, and Special Waste
Sanitary Drainage
Sanitary drainage carries sewage and gray water by gravity. Know the components and their sizing: fixture drains, branches, stacks, building drain, and building sewer. Pipes must slope uniformly at code minimums, and changes in direction require approved fittings - a sanitary tee for vertical-to-horizontal, a wye or combination for horizontal-to-horizontal. Cleanouts are required at specified intervals and at the base of stacks and changes in direction.
Storm Drainage
Storm drainage handles rainwater and may not connect to the sanitary sewer unless the code permits combined systems. Roof drains, leaders, and area drains are sized by rainfall intensity and roof area. Know the difference between a primary and secondary roof drainage system, and that trapped roof drains require vents. Storm piping must be protected from freezing and supported per code.
Special Waste and Traps in Questions
Special wastes include grease, oil, sand, and chemicals; they require interceptors or separators before discharge to the sanitary system. Common exam traps: routing a storm leader into a sanitary drain, omitting a vent on a trapped roof drain, using a reducing fitting in the direction of flow, and forgetting that a grease interceptor must be accessible for cleaning. Also watch for questions on backwater valves where fixtures are below the upstream manhole.
Worked Example
If a roof area is 2,000 square feet and the design rainfall intensity is 4 inches per hour, the required flow is 2,000 × 4 × 0.0104 ≈ 83 gallons per minute (the 0.0104 factor converts square feet × inches per hour to gallons per minute). Use that flow to select the leader and roof drain size from the tables.