"Flushing," diluting the system with liquids to mask illegal drug use before submitting a urine sample, is an easy and effective way for offenders to defeat urine testing. Drinking two or three 12-ounce glasses of water can produce up to tenfold diluted urine within 30 minutes. This article examines earlier research on the subject as well as original research conducted by the US probation office in the Southern District of Iowa in 1995-1996. It advocates measuring urinary creatinine and specific gravity to detect dilute urine samples and offers recommendations for combating intentional drug test manipulation. Alternative drug testing methods such as the sweat patch and hair analysis are currently available, but urine testing is the method most frequently used because of its low cost. Analysis of specific gravity or creatinine levels is an effective way to ensure that urine test results are accurate. Table, figures, notes, references