Hey Dave, don't know if you're still taking movie suggestions, but here's my pitch:
Puddles, containers, and graduated cylinders are the longstanding methods of judging bladder capacity, but I have a more visual idea. Since the bladder is often compared to a water balloon, why not have a model pee into a balloon? Attaching the balloon to a strategically-placed and well-fitted funnel could do the trick. Granted, you won't be able to see the pee stream or the direct source (what are we: perverts? wait, don't answer that...) but you would have the interesting visual of watching the balloon slowly fill up, and when she's finished, we should have a fairly good idea of what a bursting bladder actually looks like. It would probably be ideal for higher-capacity model. Maybe it's too gimmicky, but it's a thought.
gg111
ps. I've scanned a lot of the topics on the forum, and there's an alarming amount of criticism of your work; you should have done this, you should have done that, etc. Ingrates, I say. Don't let the haters get to you. If they don't like what b2b is doing they can take their business elsewhere.