Reservoir

The Reservoir is a location in Luigi's Mansion 3. It is found in the Boilerworks on the second basement floor of The Last Resort, located east of the Waterworks and the Storage Room, west of the Observation, and south of the Main Tank.

There is a motor where Gooigi can suck or blow on the valve in it to move the rotating bridge for Luigi to get to the Main Tank. There's a ladder which Luigi can examine to open the ladder up after draining the water and making his way back to the Main Tank. When revisited, Luigi can launch Toad to open the ladder up again. (The game resets the floor each time you revisit it in terms of the objects.)