This is an Instructable for an air tank that can be used with lego pneumatic elements for powering robots without continuous pumping. This goes along with my pneumatic snake, and my bike pump adapter instructables.

Step 1: Materials

You will only need a few things.

A plastic bottle that can hold pressure. I used a carbonated water bottle. Anything should work as long as the top seals.
A tube that your pneumatic hoses will fit over. I used some hard plastic ones that come in some lego sets.
Glue-preferably something thick. I used hot glue.
Something to make holes in the bottle cap about the size of the tubing. I used a drill but any sharp pointy object will work.

Step 2: Make It

This is a very simple process.
1. Make two holes in the center of the cap. If they are off to the side the cap wont seal
2. Cut two lengths of tubing about an inch long and put them in the holes
3. Secure them with glue.

Congratulations, you just built your first lego air tank.