Use graduated cylinders if you can't get your fingers in there. If you can, use your fingers. Anything will do, a cork, whatever - something to pee through may be handy. Make sure it's easy to clean.
Ballooning your foreskin with urine will not hurt you at all. It's released from your bladder - how could it put too much pressure on your bladder? Could work, depending on how long you can maintain it. Graduated cylinders is easier to maintain for a longer period of time - and you won't accidentally get things wet.
Drinking plenty of water is the best way to prevent UTI. Lemonade is a good drink to help prevent kidney stones. Your pee should never be darker than weak lemonade. If it is - drink.