Saintprudence If you can be trusted to stay alone in a warm bathtub for an hour, you can certainly be trusted not to wear a belt. But the bath would be a terrible temptation. Ergo, the belt should remain in place at all times.
I faced this problem not wearing a belt all the time. I solved it, pretty much, by taking showers, where one is less likely, I think, to linger. Also, I shower in a locker room where there are other people so one is limited in what one can do. Not everyone can do this but if there is some way to make the shower more public that would help. E.g. clear glass doors on the shower cabinet, showering with your sister or partner.