What should I do to pass a urine test in 12 hours?

Be drug free to start with. If you are a active user or drinker you will not be clean in 12 hours.

No matter what you try, you will show positive. Why not do what Fr Chuck advised? Get clean. I am amazed by the amount of people that get all worked up when they need to pass a drug screen. If you didn't use illegal drugs or alcohol to excess, you wouldn't have to worry about losing your job, violating probabtion, parole. Think about it.