Either way is fine, but if you have frozen human urine that is your own and you know it's clean then I would do that. Human urine will usually stay "good" for about 1 year frozen and about 3-5 days refridgerated. If its pre-employment then subbing is fine because you don't have to worry about being watched. Follow the SUBBING sticky for the method of doing it properly. Smoke Away Bro...