I used to do drug screens. Yah, collecting urine was a fun job(sarcasm). Believe me, they know all the tricks. The question is how alert the paticular sreener is. The urine has to be right temperature etc. If they supect something, they won't accept the sample and will make you do another one without leaving the facility. In some cases they have to watch. You don't have to let them; but, your employer doesn't have to let you keep your job if you don't. Funny thing is that ski resort employees are the worst. I would always have a few people quit on the spot instead of testing because they knew they were busted.