From the Super Mario Wiki
The Washroom (Japanese: トイレ Washroom) is a room in Area Two of Luigi's Mansion. After Luigi collects five Boos, Professor E. Gadd tells Luigi to go to the Washroom. When Luigi enters, he sees Toad crying in a corner. Toad says that he dropped something important inside the toilet. After Luigi reassures Toad, the lights in the Washroom turn on. Afterward, Luigi opens the toilet for inspection and finds the Key to the Fortune-Teller's Room.
The Washroom is quite cramped. Starting on the west side, there is toilet with an antique-style hanging tank, a mirror overlooking a sink, a radiator, and a medicine cabinet. The sink often contains a 10 HP or 20 HP restoring Heart for Luigi.
Ghosts in The Washroom (1F) during the blackout