sweat is the best thing. Running for more that 30-45 min will get your body burning fat not just calories. Your target should be at least an hour of constant activity. With a combination of exercise and dilusion (read other posts for instructions) you should be fine. You can also get one of the transport kits the urine sites offer off ebay for about half the price if you have a friend to pee for you. I used it once and it worked....a little weird carrying a bag of pee on your leg, but it worked. I wouldnt suggest buying the urine the web sites offer. Its usualy not tested and the guarantees don't mean crap. You could also just buy a test card on ebay and test yourself before your test....but if your still dirty it may be too late to order somthing else.

Hope it helps