Smoking Ganja isn't doing drugs sir. There's no physical dependence so technically it shouldn't be a tier 1 drug, it should be tier 3, with alcohol and cigarettes. But I do agree with you on that if it was never done, the paranoia of not passing a test wouldn't be there.
Cranberry juice has antioxidants which help, but you need to drink a gallon about four hours before you take the test for it to really do any real work. On top of that you will need a lot of vitamin B-12 supplements and some creatine supplements to make sure you don't have a voided test. Many employers take a voided test as a failure.