There's a video that's been posted in more than one thread - don't ask me when, and I'm too lazy to search for it - of a black dude anal fucking some chick, and he literally pisses in her ass.
Funny story (you had to be there): A girl I knew once asked me, hypothetically, if I would piss in a chick's pussy while fucking her, if she asked me to. I said I'd have no problem with it, but have you ever tried to piss with a hard-on? That's the trick.