man, i just play it 100% safe and get my lil bro to piss for me. I have him piss in a small prescription pill bottle (that is THOROUGHLY WASHED FIRST-you dont wanna get someones clean piss, and have them piss into an empty percocet bottle or somethin dumb like that,lol) the night before the test, but only have him fill it up halfway. keep it in a dark place over night. The morning of the test, take the piss, and fill it the other half way up with HOT water(depending on how much time you have til your test - if its only an hour or two away, use WARM water), and then put the cap on.
Then, put on a pair of boxer briefs, and then a pair of boxers over it, and take the pill bottle, n put that shit under your nutsack. The reason you put it under your nuts, is because your piss has to be the right temperature, and keeping it under your nuts not only ensures that your replacement piss will be well hidden for the job interview, but also ensures that it will be either body temp exactly, or a degree or two slightly above body temp. keep that shit under your nuts all day if you have to, but do that shit - its garunteed to keep it at the right temp.
Go to your test. Take your replace-a-piss out, fill the test bottle up with half of the pill bottles contents (it only needs to be a very little amount. They dont care as long as its past the line which is about a half inch above the bottom of the cup), and pour the rest into the toilet in a thin pee-like stream. close your test bottle, close your replacepiss bottle, hide that shit n walk out of the bathroom. WOILA! your fuckin employed.