It is a little easier to fool a drug test than a breath alcohol test. Proper drug test procedure should eliminate the possibilities of a subject switching their urine specimen with another, or tampering with the specimen. Drinking large volumes of water will dilute the urine, thereby reducing the concentrations of drugs in the urine. The detection of some drugs, such as amphetamines, is affected by the pH of the urine with some kinds of methodologies.
It is more difficult to fool a properly administered breath alcohol test . Evidential breath testers are designed to thwart the most common efforts to trick breath testing. As long as the subject delivers an adequate deep lung breath, there is virtually no way an individual can mask the alcohol in their breath. A subject who claims that their positive breath alcohol test is the result of mouthwash or cough syrup use may be asked to retake the breath alcohol test in 15 minutes. This is more than sufficient time for the remnants of alcohol in the mouth to dissipate. A second positive breath alcohol test after 15 minutes cannot be attributed to mouthwash or cough syrup.