SpudFiles

it is not for venting, but for spraying butane in easily and it is self sealing right after u remove the butane.

edit: u move the magnet out of the way and back when done.

good, but you need some gasket material around the hole to give it an extra good seal

that would help, and the combustion itself will help too.
i dont wanna spend $30 on a meter, i can make this for $5

A metal flap, so simple. The inner pressure will just push it harder against the wall of the chamber.

Pick up some of those neodymium magnets if you can, that's pretty much the only kind that will stick that hard.

http://store.yahoo.com/fridgedoor/neodmag47dia.html

3.99 for a pack of 6.