Oh I definitely don't pee in swimming pools. *shudder* After all, people are all swimming in it, accidentally drinking it, etc. Just ew.
But I definitely pee in the shower. I used to try to hop out and dry off in time to make it to the toilet but it was just too much work. I'd get water everywhere, soak the roll of toilet paper, and then waste hot water if the shower kept going without me. So I pee in the shower. Urine is sterile (at least in optimal conditions for healthy people) anyway and it gets washed away with soap. And I do clean my shower regularly.
I wouldn't care if anyone peed in my shower either. Just don't pee in my sink. I don't care if the draining system is the same. I just can't see anyone doing that without making a huge pee mess.