How long do certain drugs remain your system?

Most drug testing laboratories administer a 10-panel drug screen urinalysis. The drugs they test for are both illicit and prescription, and a positive on either can have devastating effects. The "biggie" here is marijuana because it's both illegal AND stay in your system the longest, Unlike other drugs, weed gets stored in your fat cells, and therefore takes the longest to dissipate. I can tell you unequivocally that you need to abstain for 17 days if you want to pass the weed test (using urine as the testing base), and this is true if you are a moderate user...3 or 4 times/week. But what about the rest? I'm particularly concerned about benzodiazepines (benzos). Xanax would be one such example. You read so much CRAP on the internet, and I'm interested in a definitive answer. I should think that 7-9 days of abstaining should do the trick. Does this sound right? About 5 days should cover the remaining 8 drugs (cocaine, meth, angel dust, etc). Please let me know if I'm on the right track here. And yes....I realize that frequency of use, potency, metabolism, etc all come in to play, so let's just take an "average" user with all "average" characteristics.