Take 2 bottles they should be like the EVIAN or SPRING WATER bottles.
Cut them in half, or a bit more than half.
Take the halves with the bottle opening (the side where you put the cap on).
In one of the halves put a ping pong ball in.
Now glue the 2 halves together backwards , so the 2 cap ends should be pointing outwards.
Duct tape around the center where it is glued to make sure its air tight.
Now attatch a pipe to each end then attatch those pipes to whatever you need and you have a valve where air can only go in, but not out because when its going in the ping pong ball would be rolling a the bottom, but when sucking the air out all the air is force to pull everything out with it so the ping pong ball flies to the end and blocks the cap part where the hose is connected.
i'm making a picture now.
EDIT: Picture (blueprint) This was built before.
Edited by Nerfy_BuNNy, 30 July 2004 - 01:04 PM.