This is a long in-depth process, but it's totally worth it!
The guy drinks alot of water or what not for several days, but does not piss. It will hurt and be very hard to pull off, but just go with it.
Eventually when he can't hold it any longer, the girl begins to pleasure him and while he is on his back and about to cum she sits repeatedly on his abdomen to force him to urinate while he is trying to jizz. The force on the stomach will cause to pee stream to shoot up in the air. The pain is simply Elysian.
Dude I went three days without taking a piss but it was so worth it when my ho jet ski'd me in a carnal fury.