To say the truth, I was in the situation when I needed to pass a urine test on my job. The best you can do - is clean your system, to detox yourself. I tried some kinds of detox pills and also drinks. The info over the net is likely the same on every website, I found this article www.marijuanadetox.net/detox-pills-drug-test.html very useful in my occasion. Maybe, someone else needs such a piece of advice.
There are also some other world spread ways of thc detox. Lots of different detox pills and drinks are sold almost everywhere. My friend tried this one called High Voltage Folli-Cleanse Detox Shampoo also very helpful for hair drug tests, I've read an article fmahealth.org/high-voltage-folli-cleanse/ where you could find info about preparation, instruction and even places where you could buy it. The shampoo actually works. My friend was another skeptic at first but bought it at last. The shampoo is a little bit expensive but it's worth the money. Thanks to the Voltage Folli-Cleanse, he has passed the test. I am surely going to recommend others to try it out.