You can eliminate that vacuum before you put the water in, by stove piping it. Take the plunger out of the syringe, and push it through the top. It makes it way easier to control when you reconstitute, and also makes drawing for injection easier, and you don’t have to inject air, each time to speed up the draw.
Jano disproved some of that rough handling of HGH, at least, as far as causing degradation. Not sure if that applies to everything, so I’m still fairly careful, but I also don’t worry as much about messing something up by hitting the puck with water, or shaking the vial.