Well the other day when I was picking up some 1/2 copper tubing to make a hard line for my breather tube. I noticed these really cool units called "air chambers", they are 1/2" opening that expands into a 1" X 12" canister for the lack of a better word. I was thinking of using several piped together for a vacuum reservoir. If you guys are interested I could post a photo. Is there a formula for volume or capacity on vacuum?