OSHA Standard test?

Hello, I've got to take an urine test tmw @ an OSHA construction conference. How do these tests compare to an at-home test or a test taken at the local clinic? I've got an at-home tests than measures at a cutoff level of 50 ng/ml. Will this test be accurate enough prior to going in tmw? I've been sober now for only 9 days and prior to that I smoked regularly, typically 6-12 hits a day. I've also purchased a detox drink, do I dare use this for this particular test or is that to big of a risk? Today and the days prior I have been pounding glasses of water and today I picked up a bottle of B-50 vitamins in which each tablet contains 50mg of B-2. How many of these pills need to be taken to turn my urine yellow or again is this not even worth the hassle? If the test comes back dilluted will they re-test me or just consider it a failed test, please help!