[zx10guy]

Just telling you how my last drug test went which was years ago. I don't see how you'll be able to sneak fake or someone else's pee into the test if they send you to a specific place to get it done. The process is you show up and prove who you are. They escort you to one of the bathrooms. They have you empty your pockets and make sure you don't have anything that you're carrying into the bathroom. They then wipe the toilet seat and such. I also seem to recall some sort of dye they pour into the bowl of the toilet. You're told to pee in the cup up to a certain mark and then the rest into the toilet. You're told clearly that you're not to flush the toilet when you're done. The tech doing the test will visually examine the bowel and then flush.

The cup you provide a sample in is then taken into an area where there is this machine which for a lack of a better description looks like a Keurig. The container is put into this machine and immediately analyzed. The results are then sent into a portal where your employer will be able to access the results.

I don't know about whether it's a good idea to approach HR before doing the test. If this job is valuable to you, you may want to consult a labor attorney.

ETA: I also seem to recall the sample you provide is temperature tested too.