How quickly does my body burn up thc to the point of not registering on a drug test?

It doesn't burn up: it metabolizes. A single use of marijuana will give positive tests for only a few days. A heavier use may be detectable for 5 days or more. Regular use, however, results in the metabolites accumulating in our fat cells, and they can last weeks or even months. If you are being tested regularly and continue to use, you need to consider that you have a marijuana problem and seek help/counseling.