I use a 5 gallon Craftsman portable air tank and it will get me through a paint job. Something bigger would be better except for taking up more room but 5 gallons gets me by. For filling it I use a "tire inflator" type pump (which also comes in handy for inflating tires, go figure) to pump it up to maybe 90 psi. If it starts getting low, it's very easy to pressure up.