A few years ago, I had tests for a weekly class given to me by a judge.

Water and a very, thin diet helped me. Until I went for a "fat" meal at a restaurant and my last test came up with .14 nanograms of THC. My instructor told me that, under .25 ng, usually doesn't even show up on tests. It had to have been my three-course meal. A story and an extra week of class made up for the failed test.