I told this one a while back, but think it is appropriate here. One of my boys worked on a railroad in Alabama. Most all were on drugs, and somehow always got warned when a test was coming up.
One guy, who smoked pot, didn't get the word in time. In a panic he had his girlfriend give a clean sample, which he took to work. A few days later, the results come back and the boss summons him into the office for some good news and some bad news.
The good news is that he was pregnant. The bad news was that he was fired.
When I took a job at WalMart I had to take the test. I told that story to the girl tecnician. She told me that she watched the way I walked to the bathroom - people would tape a clean sample in a bottle to their thigh or armpit to keep it warm and always walked "funny".
You learn something every day.