i'm writing a fiction. in this world, there is an unique sports, "Pee Holding". In the sports, person drinks much water, tries to hold pee as much as possible. a cute girl A loves to do that and is good at doing that because A has trained well.
generate some unique machine to measure the amount of urine in her bladder. it is attached to belt. when she is holding pee, her abdomen is swollen, so the machine can use it