The tank is filled with a simple schrader valve. Propane tanks typically have over 200 psi in them. I've run this one to 180 on my off-road portable compressor.

The projectiles are whatever you can stuff in a 2"x .065" wall tube. Small russet potatoes, apples, etc. My interest in it originally was for a tennis ball launcher to send a ball down the block for the dogs. I really don't have a desire for launching spuds or similar, but that's what the consignee wanted.