You don't do drugs! Nothing you can do, just go urinate in the cup and cross your fingers!
The only guaranteed way to pass a drug test is to not take drugs in the first place. The majority, if not all, alternative options you'll find on the internet will not work. Having said that, here are the most common methods people use to try to pass a drug test.
There are a number of detox drinks being sold over the internet that claim to help you pass a drug test. They're supposed to work on the basis that the drink removes all traces of drugs and toxins from your urine.
In reality, they're more likely to cost you a lot of money, and give you false hope that you can indeed pass a drug test.
Cheating the system
Other panicking drug users have resorted to trying to cheat on a drug test. To do this they often try to switch their urine sample with that of someone who hasn't taken any drugs.
Of course, these individuals often get caught red handed and there are likely harsh penalties in place for people trying to trick the system. Many of the drug testing facilities will be able to tell if you've switched your urine sample due to the temperature of the urine.
As an additional measure, most drug tests will require you to be shadowed by an observer, who will make sure that you're not trying to cheat.
Here's a little video documenting some of the most common drug test myths: