[Exus]

Drink one bottle of water and wait untill you are very desperate to pee.
When releasing yourself, do it into the bottle.
Now get a clothespin on your nose so that you can't breath through it anymore.

Now take the bottle to your lips and start to drink.
You are not allowed to breathe until the bottle is empty.

If you fail, immediatly stop drinking and close the bottle.
Next time you have to pee, you go again in the bottle and refill it.
Then you are allowed to drink something.
And you are only allowed to drink your own pee, until you managed to empty the bottle, where you peed in before, without breathing.