Urine Test are so east to defeat I am amazed that they still use them. Weed is not filtered through the kidneys like most drugs, THC is absorbed by the fat in your body and then slowly released to the Kidneys. That is why it can be detected for so long after ingestion. But this also means that it takes time to build up in your bladder in detectable concentrations. So all you have to do is drink lots of fluid right before the sample is given and there will not be enough THC present to detect. But the labs are on to this so before a sample can be accepted it must be tested for specific gravity. In simple terms, if your pee is clear they will tell you to do it again until the pee turns yellow.
So here is what you do. Right before giving your sample for testing, drink as much Gatorade as you can. go pee at least once before giving the sample to clear out your bladder,. Keep drinking Gatorade until you give them the sample. All they will get is pure Gatorade, but they won't be able to tell because all the minerals will make it yellow enough to pass the specific gravity test.