How long does it take for second hand marijuana smoke to clear ones system for drug testing. No joke, I was +?

I have been a 7 year and 5 months methadone patient and today I tested positive for the smallest registering amount of marijuana in a urine test. I am now aware of how the incident transpired. I share a small restroom with a roommate who often smokes cigarettes in the restroom. Of course I know the smell of marijuana, but a recent phenomena is the increased use of pipe tobacco among cigarette smokers. The tax bracket for pipe tobacco is much less so manufactures market the stuff to cigarette smokers by shredding it up finer. My walking into the bathroom on several occasions and breathing in what I thought was the lingering aroma of pipe tobacco has given me my first dirty urine test in the last 88 months. It registered 50 on the test. 49 would not have shown positive according to one councilor at the clinic I go to. Upon seeing the doctor at the clinic she took away one week of my two week ‘take homes’ [Methadone is a controlled substance and in order to gain the trust to get to take it home one must stay clean over a period of time. Working up to two weeks take homes requires being clean for one year] and is allowing me to pay for another urine test. If it comes back clean I will have my two week take homes restored and have the money refunded. If it is positive I will lose my take homes, which means I will have to go to this clinic every single day to be dosed. I am due to retest one week from today. There are so many opinions about how long marijuana stays in your system I am terrified that it might still register next week even though it was a very very small trace found from last weeks test. I can narrow down my exposure to the smoke over an 8 day period previous to the urine testing in question. That test was 7 days ago, but in the meantime, during which I had no clue there was even any marijuana around me, I have more than likely been exposed again. I have until June 11th to retest, but more than likely I will test again on my pick up day which is June 2nd. That’s 7 days from now. My room mate said he smoked weed in the bathroom yesterday. Of course now he knows the severity of the issue so is going to refrain from smoking it in the house at all. I believe him. Thanks for any help or info. Of course I am ready to hear a bunch of BS over this too. I have a sense of humor to a point.