Which manhole should be used when a pipe enters at an elevation higher than the outgoing pipe?

Which manhole should be used when a pipe enters at an elevation higher than the outgoing pipe?

• A. Wet Well
• B. Junction Manhole
• C. Access Manhole
• D. Drop Manhole

Answer: (D)

When a sewer line comes in at a higher elevation than the line it feeds into, you need a way to connect them that preserves gravity flow and avoids pumping or air problems. A drop manhole does exactly that by providing a vertical drop inside the manhole. The incoming flow from the higher pipe enters the drop shaft and falls down to the level of the downstream pipe, then proceeds through the outlet. This setup controls the velocity and keeps the flow in gravity, preventing air traps and surcharges that can happen if you tried to connect differing elevations in a standard chamber.

Other types aren’t suited for this transfer: a wet well is for pumping stations, not gravity transitions; a junction manhole is used where multiple lines join at similar elevations; an access manhole is a basic inspection point without a designed vertical drop between different invert levels.