I have seen people come through clean after just one week, but they were not consistent users. My friend passed after about 10 bong loads over 2 days. We were both pretty freaked, but the results were clean regardless. He did flush with cranberry juice for a few days prior to giving his sample.
I have tested clean after three weeks using the home tests during periods of fairly regular use (a small bong load a day in the evening before bed). I carry a few extra pounds, but am pretty active. I tend to burn my fat reserves down and then rebuild them in a 30 day period. This may contribute.
My daughters (both very lean) have tested clean in 3 weeks as well (high school sports required testing) after heavy use. They told me they only used occasionally, but I am not blind. They were high every day when they got home from school.
These are really my only experiences with piss tests. Of course, YMMV in your experience with them. Good luck in any case, but I would think you should be good in 30 days or so.