Why is is so hard for people to include height and weight? Also, you said like"maybe" half a joint a day but I would rather get a more solid smoking history. It is vitamin B-2 and not B-12 that adds color back to urine. Drinking lots and lots of water days before the test will not clean you out any faster. Drinking lots of fluids the day of the test is the dilution method. You are right, too late to exercise or else the extra THC metabolites you burn will end up in the specimen cup.