Update: I got called out for dilution three days after the test. Luckily I was able to retake. This time I substituted my brothers piss by having him fill a 97¢ plastic 3oz bottle from Walmart. Drove around with it tucked in the Nads with the seat heater on. Did it on the fly and didn't arouse any suspicion. The temp was within normal limits, so I think I'm golden. If they don't catch you in the process, can they find out by any other means that you substituted?