The narcotic ingredient in "Percs" (Percocet) is the same ingredient as in Endocet or Oxycontin. It is Oxycodone, a synthetic opioid with a longer half life than most opiates, excluding Methadone or Buprenorphine (Suboxone/Subutex). Before its popularity it was not detected in opiate drug screens because the standard opiate test did not detect it, due to its chemical make-up. However, nowadays virtually all drug screens are designed to detect it. The test do detect Oxycodone is more "sensative" than the standard opiate screen, therefore much smaller amounts can give a positive screen; combine this with the fact it has a longer half-life, it MAY take a week or possibly even longer to get a clean drug test, where as most opioid type drugs (Morphine, Codiene, Heroin, or Hydrocodone) are not detectable after two or three days. I am in a methadone program and I am going by what I was told by one of the nurses. I also have many years of experience with a lot of different opiates, especially Oxycodone. I hope this helps you, good luck!
I'm not sure what PERKS is but if it a type of drug they can stay in your system from 2-4 weeks, depending how much and how often it was taken. If its related to alcohol it will take 24-72 hours to clear your system.