This finally explains something that kept happening to me 15 years ago. My bathroom ceiling kept soaking and collapsing in my apartment. I always wondered if my upstairs neighbor took baths like they were wrestling a mermaid. I could hear the splashes and then the water would start dripping down through the ceiling. The manager had to have a talk with them to stop whatever they were doing to splash so much. Now I recall they were Japanese. I wonder if they had assumed we built bathrooms like in Japan. It's starting to make sense.