That would only work if you wanted the organism to always reach a full tank, or near full tank, before taking the action. I'd wager that's a non-ideal situatio

That would only work if you wanted the organism to always reach a full tank, or near full tank, before taking the action. I'd wager that's a non-ideal situation. Think about the times you've reached a completely full bladder...not a good position to be in. So you have a combo. Taking a whiz is pleasurable, so you do it when you can. But if you get over full, you get a nice zap of discomfort to let you know you're in a danger zone.