In a piss test, they look for three things: one, obviously, they test it for drugs. Two, they note the color. It should be really yellow. And third they will note its specific gravity by testing for the level of creatinine.
Begin taking creatine monohydrate as directed, as soon as possible before the test, as in, a few days before the test. This will make your urine heavy with creatinine.
To dilute your urine to the point that the drug metabolites in your urine fall below detectable levels, you must begin flushing with water 6 to 8 hours before the test. Soda works too, especially mountain dew since it's clear, and has a lot of caffeine which is a diuretic. By drinking about a quart of fluid per hour, you should be pissing completely clear in 2-3 hours. You should use home tests to verify your levels. Testing negative is a big confidence booster.
When you are within two hours of test time, take five or six vitamin b tablets to give your urine a rich golden color, along with four asprin. Asprin may interfere with the chemicals of the test and help produce a false negative. Continue sipping up until test time.