from my limited reading, my sense is, so long as you take the mid-stream
-meaning the first third, (* sorry: I meant mid-third) then you are not saving the part that might harbour or hold any undue bacteria.
(The last thirst is simply more dilute.)
also, don't touch whatever you use to collect the urine, to the genitals. And use a clean receptacle.
The rest is pretty standard reasoning, I'd imagine.