I'm similar size to you and very little body fat. Extremly high metabolism. Drinking lots of water before wont do anything really until the day of the test. I was clean 14 days and was able to pass a home test with a dilution and creatine.

Being 25-30 days clean of a simliar size to me, just pick up a Pharmatech home test at The Wall, use your first void of the morning (midstream), if you pass that you are money in the bank. (and probably will). Only will cost you 15 bux.