Underground waterway

SEWER

Think of the network that carries away waste and rainwater beneath city streets, often connected to manhole covers.

"Underground waterway" points to a hidden channel for liquid, and "sewer" fits perfectly as it’s a man-made tunnel system carrying wastewater beneath cities. The clue avoids tricky wordplay—it’s a straightforward definition where "waterway" hints at flow, and "underground" narrows it down. Think of storm drains or pipes you’d see in urban areas, though "sewer" is the more precise term for waste transport. No puns here, just a direct match.