I had to clean out from smoking numerous times a day in 2 weeks not to long ago. I drank anywhere from 1 to 2 gallons of water a day. I also excercised to a slight extent. I drank a gallon of water before the test and I personally passed. I have no clue if it was because my urine was so dilute or if it worked by drinking lots of water for those 2 weeks, but I figure it cant hurt to do. Exercise if a definate way to remove fat from the body and therefore the cannaboids stored in them. Drinking water will also help to clean out the blood and your entire system, but who knows about the cannaboids. I would just say drink and exercise a lot cause it is the most natural way to clean your system out and it worked for me so it has to work to an extent I say. Besides, it is cheaper than buying stuff and if nothing else it is really healthy for you.