I don’t think the kink is about drinking pee, it seems to be about someone so beautiful expressing or excreting what doesn’t seem to correspond to such beauty. It’s like you want the worst possible expression of a person, because they seem incapable of raunchiness. It’s also to see someone doing something that seems unladylike or the most intimate. It may also be the simple curiosity of knowing how someone pees or shits. That’s usually so private and compromising. We want to know everything about someone we are infatuated with. Are they real? The recipient usually feels recessive, where the other person seems to be the one with the power.