Well, I'm sure not all these steps are necesary, but I did this and passed my drug test, and it's not one of those, "I know a guy, who knew somebody, who talked to this kid's sister who heard that this works," stories. It worked for me, and still do it for probation. I try not to smoke for a week before the test, at minimum three days. Drink as much water as you can, and during those three days take niacin to help clean you out. Then, the day of the test drink and piss as much as you can. About one hour before your test, drink at least a gallon of water and piss as much as possible. Before you leave to take the test, you have two options, I have tried both to success:
1. Take a glass of water and bleach. Dip a knife in the bleach three times, and dip it in your water and drink that, but make sure not to piss after doing this, to hold in the bleach.
2. The same as said before, the vinegar.
Now, all those steps may be unnecesary, but that's a method i developed and passed my first test with, so i stick strictly to that each time now, and try not to change it much.