Never, ever fly an aircraft with an endurance greater than your bladder capacity!
I agree that one should never fly with a very full bladder - among other things it is a distraction, and it can result in serious injury in a heavy landing / accident if it bursts (literally). However, being an aged glider pilot, with limited bladder capacity, flying cross-country flights of typically four or five hours - well beyong my bladder capacity - I make suitable arrangements - as do most cross-country glider pilots. In my case I choose to use aids for the incontinent which involve a sheath, a short tube with leakproof connector and a couple of 1 litre leg bags which I empty after landing. Because they are so widely used in gliding the BGA shop sells them.
There are other solutions which are more Blue Peter like involving half a washing-up liquid container fitted to a tube that exits the glider near the wheel. Sadly these can result in corrosion to the undercarriage, they also don't work at high altitude if the OAT drops below zero so one is left holding half a washing up liquid container full of liquid with no obvious solution to the problem!