Hey there, I'm a young adult looking for work too. Your rights deserve to be respected and glad I'm not the only one trying to navigate wearing diapers. You only have to disclose it as a medical condition to get the help you need.
You could possibly say something like:
"Hello, I'm here to discuss a medical condition have that requires some workplace accommodations. I've been diagnosed with urinary incontinence, and it's medically necessary to use protective underwear for me to manage it. For me to do my best work, I need the ability to take frequent restroom breaks as needed.
Also, if possible, having a discreet location to change with my supplies would be very helpful. I have a doctor's prescription/note that I can provide if needed. I am committed to my work and will do my best to manage this privately and professionally."
You don't have to share all the details, only what you feel comfortable with. Hope this helps?