Time. And then more time. It also depends on how much and how often you smoked. As you probably know, THC is stored in the fat cells of the body. (hangs around a while). Don't smoke anymore, drink plenty of fluids to dilute your urine. The tests now can determine if the urine is diluted or if you are (flushing). So thats dangerous also. If you're a regular weed head and smoke often and the weed is potent stuff, it may take 2-3 weeks for your urine to come back clean. There is a tolerance allowed for THC because the body produces it. But that tolerance level is not very high I assure you. Good luck.
unfrequent users can eliminate thc in one week.frequent users can eliminate it in more or less time depending on the metabolism.skinny people have fast metabolism and thc deposits in fat cells.so if you're skinny you might be lucky and get rid of thc in a week or two.you can take the test and do it at home.you can also drink a lot of fluids and urinate as frequent as you can.this will dilute the thc and eliminate it faster.eat protein food like red meat and exercise.aspirin and vitamin b also help.you can take the srpirin within few hours before the test.that's all I know...good luck!and no smoking until after the test:D