With your stats and low body fat and physical job you may just need to adjust your diet. Drinking excess fluids will not help but if you drink your daily recommended 64oz that should be OK. Go to a high fiber diet including lots of veggies, salads, pineapple, apples, carrots, celery. Also start taking metamucil capsules, it will help a little with thc elimination.

Since you have time, I also suggest buying some thc testing srips on line so that you can check your voids and see where you stand. Your morning void is the best indicator since it has the heaviest concentration of thc metabolites. If you pass that then you should be good to go.