In a combined sewer system, every ______ shall be installed above the cover of the nearest manhole.

In a combined sewer system, every ______ shall be installed above the cover of the nearest manhole.

• A. fixture
• B. pipe
• C. vent
• D. trap

Answer: (A)

In a combined sewer system, backflow is a primary concern because stormwater and sewage share the same main. If the public sewer surges, wastewater can push back toward buildings. Installing every fixture higher than the nearest manhole cover creates a practical height barrier: backflow would reach the manhole first, and interior fixtures, being higher, are less likely to be entered by that backflow. This helps protect the interior from sewage intrusion during surcharges. Pipes, vents, and traps each serve different purposes and do not provide this elevation-based backflow protection. A pipe is just a conduit, a vent supplies air to prevent siphon, and a trap seals against sewer gas; none of these by themselves address the risk of backflow from a surcharged combined sewer the way elevating fixtures above the manhole does.

In a combined sewer system, backflow is a primary concern because stormwater and sewage share the same main. If the public sewer surges, wastewater can push back toward buildings. Installing every fixture higher than the nearest manhole cover creates a practical height barrier: backflow would reach the manhole first, and interior fixtures, being higher, are less likely to be entered by that backflow. This helps protect the interior from sewage intrusion during surcharges.

Pipes, vents, and traps each serve different purposes and do not provide this elevation-based backflow protection. A pipe is just a conduit, a vent supplies air to prevent siphon, and a trap seals against sewer gas; none of these by themselves address the risk of backflow from a surcharged combined sewer the way elevating fixtures above the manhole does.