A few different things can be done to invalidate a drug test, if there is a presence of bleach or alcohol in the urine. If you find a way to add a few drops of bleach in the urine or alcohol the test becomes invalid because it is considered contaminated. I have also heard of tests failing for the simple fact that there was a piece of hair in it. Then again that was in the military where the labs follow strict procedures. Of course your local clinic performing a simple 10 panel dip in drug test will not even know the urine was contaminated