water loading is the only method that works for sure if you're broke. if you've been any number of days clean, you can hang on the remainder, even if you did get an extension. don't smoke anything, load up on water. don't worry about drinking water ahead of time until the day of your test. do NOT under any circumstances, give your first pee of the morning. this is the dirtiest pee you can give them. test LATE in the day and load up on water during the hours before. you'll be peeing almost pure water by the time you test. forget niacin and B12, all that does is color your urine yellow - it does NOT detoxify you. if it makes you feel better taking it and you have it on hand, by all means, take a couple. even a daily multivitamin. things like bleach, salt, vinegar, vitamin C, visine, etc, don't work, so don't bother. And subbing your pee with someone elses is too risky. too complicated to prep for it, and if you get caught, you're done.

what causes false negatives are things like too much tylenol in the system, plus some other otc drugs i can't think of at the moment. your best bet is to simply water-load. i passed 4 days after i last smoked using water method.