For adding the water I do not worry much. Angle the needle toward the side so it does not hit the powder straight on, though the issue is smaller than some claim. For drawing, inject the same amount of air into the vial first. Some disagree, yet it seems no different from venting. Rarely I have pulled the plunger out of the syringe after adding BAC to release pressure, but usually I just add air with each dose instead.
The vacuum in the vials causes problems for me during reconstitution and drawing. It pulls the BAC water in fast, causing fizzing. Drawing is inaccurate because the plunger gets sucked back. Should I vent to release the vacuum, or keep it for preservation or another purpose?