The clean urine is the best method, I still recommend dilluting just incase you cannot drop the clean urine (observation etc).

If you are going woth substitution, I CANNOT STRESS ENOUGH, dress professional.

A friend and I just went in today both dirty, he failed (got caught), and I passed (subbed succesfully =) ).

The difference, he had long hair, beard came in in a t-shirt and jeans, I was in a dress shirt with tie slacks and dress shoes, and a clean cut.

He got frisked, I wasn't even asked to empty my pockets. If you look like a stoner you will be treated like a STONER.

If you got the clean pee though, DO NOT RISK USING YOUR OWN IF YOU CAN.