Laundry Room (Basement)
From the Super Mario Wiki
The Laundry Room is a location in Luigi's Mansion 3. It is found in the Basement of The Last Resort. It is west of the Service Hallway and southwest of the Garage. The Laundry Room contains three washing machines (one of which is invisible), two sinks, and three dryers, one of which contains the green gem. This is the first area in the basement Luigi explores, as well as one of the first areas he explores in the game.
After Luigi drops through the laundry chute while being chased down the RIP Suites hallway by King Boo, he ends up in the Laundry Room, where he is awoken by Polterpup. Luigi must follow Polterpup outside to the Service Hallway, then to the Garage, where he finds the Poltergust G-00.
Little treasure can be collected during Luigi's first visit in the Laundry Room. There are two coins in the left washing machine, and another coin in one of the sinks. There are three coins between the middle and right dryers. After Luigi gets the Poltergust G-00, he can suck up the Bills and Gold Bars found on the shelves. There are also two gold bars under the sinks, as well as coins and bills under a pile of towels near the sinks. There are also coins in the fire extinguisher and coins in a pipe above which Luigi can get by turning the valve all the way.
Luigi can also use the Dark-Light Device to reveal another washing machine to the right of the others with a lot of money inside. Finally, some treasure can be found in the left and right dryers. Luigi can open them by using a Suction Shot on the covers. There is a green gem in the middle dryer which Luigi can get the same way. There is a hidden crack in the far northeast corner that Luigi can look through to see the red gem.
Occasionally, towels will drop down from the laundry chute into the laundry bin in the southwest corner.