I've noticed if there's oil in the actual pin, that counts as 1/10th of a cc (if the pin is 1.5 or 2 inches, if its 1 inch then its less than 1/20th of a cc). The first time I ever pinned test e, I went through a 10ml vial in 4.5 weeks, because every time I'd get 1cc, I'd leave 1/10th of a cc in the pin, wouldn't replace the pin, and just inject. So if I drew 10 times, 1cc at a time, I was really drawing 1.1cc, and those 0.1cc's added up to 1 full cc at the end.
As for pushing all the air out, I used to do that, but now just leave .1cc of air in the syringe, no oil is left in the pin itself. You hear a "psst" sound when all the oil goes into the muscle, and you know there's no more left in the pin or syringe.
In the long-run it doesn't make much difference if you get ALL the oil, but I do it this way and its been working pretty well for me.
I know its my first post and I don't have any credibility here yet, but I hope my $0.02 helped a little.