Just my imagination, but...

Regarding the plumbing situation in the mansion, other than the kitchen and laundry room, I imagine it's something like this... On each floor: Rooms with doors facing the hallway and the bathroom are likely changing rooms. Rooms with doors only facing the hallway are the mysterious (?) WC (Water Closet). The room with a door facing the main bath on the 1st floor is probably the sauna that Bosky loves, and next to it, separated by a wall, is likely the bathtub for the cold bath. The bathroom on the 2nd floor is probably exclusive for the (female) master. It's a mystery why there are two bathtub-like things. If there's a private sauna hidden behind the "Bathroom" sign, it might be for the cold bath, but if not, perhaps it's a herbal bath concocted by Professors Amon & Lucas? 🤭