You will be fine for this. A part time toker can smoke a bowl (that's what it sounded like) and be clean in a 2 or 3 days. If you menat smoke one eigth you are still fine. If you really want to be sure drink half a gallon. This will dilute what's left and leave the gravity high enough. Just don't smoke again untill you know you past. If you are working for a couple weeks your in the clear. But don't as if it's done!