THC is stored in your fat cells so pissing alone won't do much. but working hard and exercising will break down the fat and you will pee it out.
so just exercise alot and drink alot. the day of the test don't lift a finger as to not burn fat, also drink a ton of water right before the test, piss, then piss again for test.
and not smoking would be wise, your just asking to fail by pushing it