One thing I thought about the blue liquid is that it could be like those chemical weapons, where a tiny amount can wipe out a lot of people in a fairly large area, so a few vials of the stuff might be enough to clean up. The scene mentioned where he jams a vial into an Alien's mouth could be an act of desperation, as I doubt he's going to walk around forcing vials into thousands of individual creature's mouths, there's no way that could work.