Sewer valves are water-controlling devices found just south of Ardougne. They are used in the Hazeel Cult quest. There are 5 sewer valves total. Each has a "turn-right" and "turn-left" option.
Just east of the Clock Tower is a dungeon entrance. Inside there is a raft. When boarded, this raft goes to different places based on the positions of all 5 sewer valves.