Just tested myself, failed after 26 days cannabis free. I think it takes me about 45 days or so, and i'm 6'3 185lbs with low body fat. My girl is 19 days clean, and passed and shes quit thin. The difference is our usage patterns, she was at .1g per night, and I was about 1.5g from morning until night.
I'm just thinking I should wait until I self test clean, then freeze some urine? On the day of testing thaw out to room temp, and use that since they don't watch me in the bathroom? How could that not work?
Urine goes bad but not sure if freezing it would negate that or not, my amateur opinion is that it should totally work in theory unless the cold/time does something to urine I'm unaware of.
I've also always heard that CBD will spark a positive test. Not informed enough though.
Glad you are getting the help
@Aimless Ryan , next time if you are worried load up on creatine in the days before the test. Standard flushing works for dip stip tests but lab tests, they test for vitamins, buoyancy, creatinine content (metabolized creatine). And load on B vitamins.
And then flush accordingly. Your urine
should pass a lab test but YMMV. It's because you are basically pissing out straight water but they can't tell because of the excess vitamins/creatinine. YMMV but I've known people with success with this.
For example: lets say your body breaks down THC at 60 milligrams per hour into your bladder waiting to be disposed (arbitrary numbers) and lets say that the test comes up positive at 60 milligrams. After an hour and you piss once, that piss is going to have 60 milligrams of THC.
Now if you are flushing, that first piss after the hour will be dirty (60 mg), but every subsequent piss will be emptying your bladder faster than your body can leech THC into it. Say now instead of an hour you have to piss again in a half hour because of all the water, now your piss is only at 30 mg, etc, etc. Working out is actually horrible to do right before a test because it causes more to leech from fat into bloodstream. If it's up in your fat and not in your piss, thats ok! If you keep pissing your bladder can never have enough THC in it to come up positive.
And that's why you load up on the extra stuff too because if you have extra amounts it will leech into your urine to an acceptable level and appear that you aren't flushing. Hope that makes sense I am not a scientist
Edit:
@steama nice article, great minds !
I've never seen those before! Then again my urine testing is usually for other things! 
