If drug testing is a condition of your probation, and I'm assuming it is, you have to comply or face the consequences of jail time (or at a minimum losing the benefit of Prop 36 or Drug Diversion) Unfortunately, i don't think the judge will readily accept the notion that EVERY time you go to the P.O. you can not urinate. What about sitting in the office until you have the urge? What about seeking the test at your doctor's office? While the latter option could end up a costly undertaking, it would at least suggest your good intentions of complying with that condition of probation rather than what it appears to be - that you are refusing to comply. Good luck.