My little boy has to have an ultrasound on thursday and needs to have a full bladder, but how can I do this? He's not properly potty trained due to problems with bowel movements which is currently being investigated. But will happily pee in a potty, and pull pants up and down. But how do I make him not wee? Surely if he has a full bladder and I wont take him to a toilet he will just pee his pants. Anyone with experience?