Stacks:

You'll be fine from the sounds of it. I just subbed a few weeks ago for a pre-empl non DOT test and it worked out well. The workers at most clinics don't give a shit about you passing or failing, and typically don't care enough to really be anal about it. There could always be that one real vigiliante worker who makes it their business to hawk over you intensely out of some perceived 'moral' duty but that is very unlikely.

I got a friend's clean pee, put it in the urinator (but I'm sure a condom or shampoo bottle would be fine with warmers) and emptied it behind the closed door. WHen I came out it was pretty clear that they weren't listening or watching and it was pretty routine. Just get in the mindset that you are clean just like everyone else and act that way. They don't EXPECT you to fail or tamper, so keep that in mind and act that way.

Go in there and own it, you got this!