If you have any basic knowledge in chemistry or biology you will know that enzymes (proteins) metabolise (change) the substance you've consumed. The changed substance (metabolite) can be further processed by other enzymes or excreted from the body. What you first must consider is the enzyme that acts on your drug of choice and, furthermore, the enzymes that act on the metabolites. Let's take benzodiazepines for example. The enzymes that metabolize these compounds are CYP450, CYP3A4, and CYP2C19. If you want to increase the clearance time of benzos from your system you need to induce (increase activity) these enzymes. Let's say you took the benzo nitrazepam, an inductor of choice for this drug would be (if you could get a script for it) is rifampin (an antibiotic). There are even OTC things that can help with inducing metabolism (i.e. St. John's Wort). These would decrease the half-life of the drug and consequently increase it's excretion. You must also consider that you aren't taking any drugs/foods that could inhibit enzymatic activity. A word of caution about increasing benzo metabolism is you can also increase blood level concentrations of active metabolites. Do some digging on your drug of choice and it's metabolism. I just thought I'd make a shout out about this. Note that there are other basic factors as well like drinking lots of water over an extended period of time if your drug/metabolite is water soluble (preferably water with electrolytes i.e. tap water cause you don't want to die from lack of essential electrolytes), cardiovascular exercise get's things speeding up too. Here's some links for more info to get you on your way to peeing clean.
http://www.aids-ed.org/aidsetc?page=cm-314_rec_drugs
http://www.thedrugmonitor.com/interactionstable.html
http://books.google.com/books?id=ngm...l=en#PPA835,M1
Do some research and empower yourself so you can get/keep that job or stay out of prison.