This is a very simple pressure air tank for lego pneumatics. I thought of this after I built a lego air pump and saw how expensive lego pneumatic parts were. It's made of a sauce container I got at a chinese restaurant, a T pneumatic junction, and glue. It isn't tested and I have no idea if it will blow up under pressure or not, but I think it will work for lower pressures. I will get back to this Instructable after I test it.
Be sure to check out the Instructable for the electric air pump
Thanks for looking!