Resident Evil 2 What is the darkroom sink for?

After entering the room, take the map from the wall to the bottom and go down two steps. Push three wooden cases into a row, and the boxes can be pushed out from the inside.

Press it, pull the switch, and then walk from the wooden box to the opposite side to get the key. Go back and get the acid bomb from the other room.

Go back to Lyon and give it to him: keys, acid bombs.