Then you leave the sample at the testing facility before the process starts.
If from some reason you have to leave the testing site before providing a sample, then you better have some good excuse because that can be considered as a refusal to take the DOT drug testing, and can have some serious consequences on your employment.
So, once you are tested the results from the DOT drug testing will be sent to a medical review officer from the lab.
If you are “clean” then you have nothing to worry about but if not, then they will contact you asking about any possible circumstances for a positive result and then contact your employer.
So be well aware that there is no lay in this thing! Don’t think that you can bring apple juice for a sample!
Few days ago a friend of mine who work in logistics as an HR, was telling me how one of the job candidates that was going through a DOT drug testing brought a urine sample that was not his!