When you give the sample, don't put the start or end of the urine
stream into the cup.
While half-life tells you apprx how long the drug may be active in your system, the metabolites from drugs can be detected for days or weeks, depending upon the drug. Opiates such as hydrocodone, I believe, are detectable within 2 to 3 days of use. There are many sites on the web, including those of companies selling drug tests, etc.