Dude you have nothing to worry about. If you really smoke as little as you say you do, you would pass a drug test in as little as 10 days after you last smoked, as long as you dont smoke a shit ton when you do smoke. But generally if you smoke less than an eighth you would fall into the 10 day category. Trust me I have many encounters with urine test in my chosen career. We'll leave it at that, let's just say I would be the one giving you the drug test if you were on Probation.
I'm no angel myself, just come off that way to the public.