I have only ever done this if there is a bath to do it in otherwise i would never risk or want to do it anywhere else too yucky and too much hassle.

Double shower could work but now days i turn any requests down for it as too much hassle. I am more a basic provider now days.

Nope, it's like trying to pee in the sea for me, my brain won't let my bladder do it.
I did do it in the bath a few times many years ago with a partner but can't seem to manage it now I could make ££ from it, no matter how much water I drink beforehand.

Well, believe me, ANYTHING can be learnt... In the case of pissing, I suggest to try and avoid thinking about it, but relax and pretend to be alone, at least initially...
I sincerely wish you luck, once you overcome the initial hurdle, the rest of the way is all downhill!