The best for you.. over a week or so would be to drink about a gallon+ water daily and run/work out consistently to induce breakdown of the fat cells holding THC, and flush 'em out! Do drink plenty of water.. but don't fret too highly..

It is well known that light users can metabolize THC at a much faster pace than avid tokers.. your levels should be relatively low even now.
You may want to invest in the Whizzer mentioned.. but a little faith and activity should do you well. If this job is important, as I assume it to be.. consider the Whizinator for a 'no-risk' result.

A drop of bleach in a sample of urine can do the trick.. however if anyone mentions this pay no heed.. many containers test for bleaching/sanitary additives.