The fantasy diuretic is some form of drink/beverage that has extreme diuretic effects. Within an hour drinking even just a little bit of it, the character(s) who drank it will need to pee desperately. No matter how large or strong their bladder the diuretic will quickly fill them to bursting and they will simply have to pee, voluntarily or not, the pee will be coming out. Characters effected may release significantly more pee than is realistic or possible. The character will continue to produce and release huge volumes of piss, their bladder filling impossibly quickly, making them need to pee huge volumes multiple times per hour. The effects can last for an entire day depending how much was consumed.