It's difficult sometimes when you've met them already, you know they're not gonna hurt you, they pay well, but something about them makes your skin crawl, and you just feel a bit disgusted with yourself after.
I wouldn't normally talk to a client when going for a pee, only one who is into WS do I speak to, and he watched me on the toilet! Just ignore him or turn the tap on/sing while you're having a wee.
Disagree that you shouldn't be allowed 'breaks' when with a client for a long booking too. I don't smoke, but if I did, I think it'd be ok to have a break for one.
It's after 6 now, did you do the booking, and how did it go?