"Yeah, no. See I really need to go, and there's a line, and it's all just quite the mess out there. So..." You say improvising a reason as to why you walked into this stall. You could have just said you felt like it and were allowee to do it, but that would become boring if you overused that excuse. Plus, when doing things this way, there is always a potential for something unexpected to happen, or at least you hoped it worked like that.
"Fine, just let me push this out for another few seconds, then I will take care of your pee, so please just be patient." Said the girl. She turned around on the urinal so that she now was facing you, while she leaned downwards so that her pussy was still angled into the urinal. Then she opened up her mouth, while she pulled down your panties. Next she put her hands on your ass and pulled you in closer until her mouth made contact with your pussy. You could feel her tongue spread apart your lips. Once she had you opened up, she gave you a thumbs up and you began to pee into her mouth.
Interestingly, as you peed into her mouth, her own flow into the urinal which had been slowly loosing its force redoubled in its pressure. It took only about 15 seconds for you to empty your bladder into the girls mouth. When she felt that you had finished, she used her tongue to clean up any of the remaining droplets. When you were all clean, she removed her face and pulled your clothing back up for you. "Wow, your diet is really good. Maybe drink a bit more water, but aside from that, I couldn't find anything that you should be concerned about in your urine. You are not pregnant, nor do you have any STDs. And that's all the info I could aquire. Feel free to use me again whenever you feel like something isnt right, or are just curious." The girl said.
"Wow, your quite informative aren't you." You said to the girl. You were rather impressed by how much she could tell about you just by drinking your pee. "Of course I am. I am a urinal girl after all. I've had pleanty of practice by now servicing high school girls like you who don't mind a little perversion in their lives. I am glad that our school allows seniors to practice any of their fetishes as long as they do not harm others permanently or without consent. I have a pee drinking fetish, thus I joined the urinal girls club."
Damn, this is awesome. You knew you made the right choice of not using the easy excuse. Now your school openly allows seniors to learn, practice, and/or take part in their sexual fetishes. You were now very curious about what other fetish clubs existed. Maybe something kinky like a bondage club, or perhapse something more extreme, like a club that trained girls in how to become proper sex slaves? Or you could even create your own club using your power that allows you to do anything. This was something you would need to look into.