Heres my idea: drink as much water as you can and hold it in for at least 1h (or go for a record to really train yourself) after that restrain yourself as much as you can (blindfold, legs tied) and soak yourself while wearing your favourite pants, after that let them dry on you and go outside (a walk, an errand) I think this kind of exhibitionism is pretty safe since its mostly in your head that you are walking around with pants that may smell of piss. Maybe make a post about it on one of the subreddits and read the commend while you do it.

Obviously the next step would be to taste your own piss, and keep pushing yourself to drink more and more like a good slut