What is said in a tub disappears from the screen when the last person gets out. Nobody can scroll back. The park keeps a private copy that never appears in the product, so reports can be checked.
When a tub is empty, the Rober is in it. Ask and he will tell you he is the host, and a computer. He says goodnight when a second person gets in.
The water is changed after close, at 04:10. Every tub, every night. Pruney is not a rule, it is a warning.