How Long Does Valium Take To Clear From The System?

I have been diagnosed with anxiety disorder and panic disorder. But i stop taking my meds a couple years ago and this past week ive encountered alot of stress. I no longer have have a valid prescription to my meds. A friend gave me a valium and the only thing stopping me from taking it is the random drug screens my job gives. I to know it is something they test for, i was wondering how long does it take to clear my system? Its only a 5 mg tablet but i dont want to take it if i will risk having it in my system for an extended period of time.