PVC Pneumatic Potato Gun

I have always been interested in PVC cannons. When I was 10 I tried to make one using a old nerf gun and a bike pump. Needless to say it didn't work, it leaked to much and fired nerf bullets about 3 feet. But now I have been re-introduced to PVC cannons because of the "launch it" contest and wanted to make a nice potato gun for universal use. For example I could just use the tank of the gun for a air tank. Or I could convert it into a combustion cannon. (Look for another instructable in the future about that!) or it could shoot tennis balls. It's a good potato gun and is pretty versatile. Thank's.