Seems to me that this isn't going to work. In order to have a complete vacuum in the mold bag (top bag) with no air bubbles then you would have to have a completely closed system. By this I mean that there would have to be no air in the reservoir (bottom bag). If there is air in the bottom bag or if you were looking to do this over a bucket or something you would then have air moving up into the top bag to replace the void of the water. In a closed system I don't think you are going to find gravity, your only force, creating enough of a "vacuum" to do what you are looking for. Please someone correct me if I'm wrong, I have no experience in Vacuum Bagging, just throwing out what I think is possible.