What is the maximum vertical length allowed for indirect waste piping and local waste piping handling sanitary wastes?

• A. 10 feet
• B. 15 feet
• C. 25 feet
• D. 35 feet

Answer: (B)

The main idea is that indirect waste piping and local waste piping must stay within a limited vertical distance to protect the trap seals and ensure proper venting. If the vertical rise from the fixture to the point where the waste can vent or connect to the drainage system is too long, the discharge can create a suction effect that siphons traps or prevents air from breaking the flow, leading to trap seal loss and possible sewer gas issues. Limiting this vertical length to a modest distance keeps the waste flow within the venting capacity of the system and helps maintain effective drainage and odor control. That’s why the maximum vertical length is 15 feet. Longer runs would increase the risk of siphonage and poor venting, which is not acceptable for sanitary wastes.