Young Buck -- Judge Not that Pee-o'd Over Fake Urine Test

Young Buck will not be going to prison for playing dirty with his pee.

Buck was facing 5 years for trying to pass off someone else's urine as his own during a random drug test in his weapons case. He brought someone else's pee to the probation department in a plastic bag and tried to pass it off as his own ... but he got caught.

The judge showed mercy, agreeing with prosecutors that rehab was more appropriate than prison. As Bossip first reported ... Buck must complete a treatment program, 100 hours of community service and pay a $7.5k fine.