I think your good anyway . Its been a few weeks . The best way is to home test yourself . A chronic smoker , like myself , naturally eliminate t.h.c. faster then occasional users . When I was being drug tested weekly , I took one big hit a week , on saturday and held it as long as I could , and got stoned as hell , but was always negative . The products on the shelves true dilute your urine . They also add a diuretic , vitamin b2 , and creatine . Creatine levels are how they check for dilution . So you can make your own , and check your self with a home test that's test for dilution before you go in . If nothing else don't give them your first piss of the day . If its been three weeks since you smoked , and one bong hit your clean now , just spent 19 dollars and test yourself . Good luck , but you won't need it . The reason one hit won't show up is you need to smoke multiple times to overlapped levels into a half life situation .