How long after smoking weed does it take to have clean urine. The most common period of time is anywhere from 3-30 days, depending on your metabolism and the amount that you've smoked.: I had to gain weight and I am fine now. It has been six weeks since I have had any canibus..How long before I check out clean on urine test. I have a physical for emplyment in two days and will have urine test. A: Cannibis sticks to sticks to fat, keep in mind.