Well, for starters... You could read the thread that says "The Official How To Pass A DT" at the top of the page...
Or you could run a search...
Or both...
http://forum.grasscity.com/seasoned-tokers/36557-offical-how-pass-dt.html
Go to GNC, buy a bottle of 500mg Niacin. DON'T GET THE FLUSH FREE/TIME RELEASE KIND!!!
Eat 2 a day, with something light, and drink LOTS of water - as this will help with the burning and itching associated with such high doeses of Niacin.
The day before your test, DON'T EAT ANY NIACIN, and keep drinking water to lower the levels of Niacin that are already in your system. The day of your test, just drink enough water to piss a lighter yellow. You're clean by now, so you don't gotta worry about failing. Just to be sure, take the sample from the middle of the stream, and piss a few times before you go for your test.
If you stick to this, and don't smoke any more until after your test, you'll be fine.