the way ive done it over the years and never got an infection is..
i take the vial and put a needle in top, not the syringe, just the needle, this will vent the vial.. then put the vial in the water that you already have boiling in a pan on the stove burner... let it sit in there for awhile then after you take it out, let it cool before you inject it, or you will be hurting.... hope this helps..