Adulterating Another strategy is adding a substance to the sample that nullifies the urine test. People have tried lye, salt, household ammonia, bleach, soap, and Liquid Drano®. Each has problems and effectiveness is far from guaranteed. Table salt and soap are the most reliable. Salt can be carried into the test site under the fingernails. However, Federal Guidelines require that the hands be washed in the presence of a monitor for just this reason. In more casual testing settings, adulteration can be relatively easy. Tampering can be detected by testing the pH of the sample, but this is rarely done--except when suspicions have been aroused CBD oil.