I would like to give full credit to Household hacker for this idea. Although mine is slightly different it's still the same concept. Anyway this project is super easy and I learned a lot about valves during the project. The project was all free for me as well so happy days.

Step 1: What You Need.

You need everything in the photograph which includes;

A Drill,An old valve + nut,
A strong adhesive or putty (just make sure it can withstand the pressure...approx 80psi),
An air can of course (you can either use an old can, buy one or ask for a spare one from a computer repair shop),
Paint (purple).

Lets get started :)

Step 2: Step 1

First make sure there is no air left in the can to avoid complications. Once you have that done drill a hole in the side or bottom of the can for the valve to be inserted. If you choose the bottom make sure it sticks out enough to be able to pump it up and also that it doesn't interfere with the stability of the can. Also think about where your putting the valve as seen below. Make sure when you go to spray the can the valve is not sticking into your hand. The valve I had was jutting out at the end so I cut that off with a hacksaw (See pictures). If you have a nut it will help A LOT . It will ensure the valve does not fall into the can. Increase surface area for when gluing it in and also will tell you how much of the valve you need sticking out so that your pump can grab onto it.

Step 3: Step 2

Next secure the valve in place with a strong putty or glue. I used ''007 Adhesive and Sealant''. It needs to be strong enough to hold in the pressure about 80psi. Seal all gaps to ensure it is air tight. Once cured make sure it works by filling the can and give it a quick try. If everything works you now got yourself a refillable air can.

Step 4: Step 4

To finish the can basically do whatever you want with it. Bring out the artist in yourself. You can decorate it , paint it or customize it. I was think of using card but decided to use the last of my purple acrylic paint. Wasn't happy with the finish but I think it was because my brush was too hard but hey...what the heck it still works and is a pleasure to have handy.
Hope you enjoyed!