(first post--mercy please)
Great thread and some very insightful discussion My thing is peeing, although not so much the "lying in a bathtub" scenario as a diverse series of fantasies I've crafted over the years. They range from the more voyueristic (elegantly attired woman leaning against an alley wall pulling her dress and panties to the side) to the more ... uh ... intimate (peeing inside someone while fucking them, and assorted follow-on activities).
Have had some interesting Golden Moments. After a mixed sex/smbd session, I was skull fucking my sub, who was not being succesfull into getting me to my third pop (ah! the younger days, when anything was possible). I was hard, but not cuming - and had a tremendous urge for something to shoot out of my cock. I also had a partially full bladder, and so started to force that out through my engorged cock and into her mouth. Felt almost as good as cumming, and lasted a great deal longer. Made my self stop, part way (oh the pleasure/pain of holding back and still needing to pee) so that she could use a cup to drain the pee into, and then started up again. Her sucking, my peeing, and her moaning as she would spit it into a cup "My God, So Much PEE!". Later I used the 3 cups of pee to pour over her head at the end of the session while telling her what a bad girl and slut she was. This is something that I have and will continue to repeat whenever given the chance.
Something I have only done twice, and rather doubt I'll do a third, is to be greeking au nautural and after cuming not pull out immediately, but instead to maintain a gentle motion, just enough to keep one semi-hard. While in this state, and still deep inside, take a good long piss. The first time I did this my partner yelped, ground herself back onto me hard, demanded my hand fuck her cunt, and came violently and in long waves. After become totally exhausted, she relaxed onto the bed, and cleanched her ass checks together and asked me to gently slip out. She got up and went to the bathroom and never lost a drop. (She also asked me to come into the bathroom, wash myself off, and let her suck me while she slowly evacuated herself.
The second time was nowhere near as succesfull. The girl was nowhere near as kinky, and simple freaked out with what I was doing. She was leaking fluid as soon as I started, and insisted that I stop and pull out. She also had no control after I pulled out, and barely made it to the bathroom, a dripping mess.
The only time I have received (and enjoyed) GS is standing up in the shower while fucking. THAT was extremely hot.