Paraphenilia stores sell shit that's suppose to work. One time I used this orange flavored stuff and you have to drink a lot of it a certain number of hours before the test.

In a management class I learned that it is really expensive to drug test. They have to test for each category (all pain killers are in one category). They are most likely to test for cocaine. Since it is expensive they usually choose to test every 20 people, the number depending on the company. So this is why peope using pass tests.