The car uses a hydraulic pump for assisting the brakes, it does not use vacuum. I would likely use a plastic reservoir you are talking about for holding the small vacuum needed to stop the engine. I just wanted to be sure that the vacuum pump would not be working against the reservoir trying to pull and pull more air from a closed system. I don't know if it needs to vent or if it regulates itself internally. (ie if the pump operates normally at 22hg, would it maintain itself at 22hg until the engine is stopped or reservoir is evacuated, or will that 22hg compound itself and compound itself?)