Yeah I researched this when I had to pass a drug test to work transport ambulance in college and I had smoked a bowl the month before. You just have to be below a specific parts per million for metabolites and it's achievable through dilution, though the external bladder method is the most fool-proof/reliable. 1) Take creatine tablets for 2 weeks before the test (if you fail for color they check creatine levels as a barometer for dilution). 2) Never give them your first piss of the day (it's loaded with the all the sediments/metabolites from the night). 3) Take a lot of vitamin B (for the yellowing to make your diluted piss look normal). 4) Drink a ton of water before the test (the actual dilution). 5) Don't burn any fat the day of the test (limit the metobolites present). Ps. Fuck lab corp and all this corporate big brother shit.