I took 2 empty cans and drilled holes in the bottom then got 2 brass valve stems for light truck wheels and used thick solder and a propane torch and soldered the valve stems into the cans
then I fill them with my large air compressor thats in my garage. now I never have to buy those exspensive cans of air. just be carefull when filling the cans and make sure the valve stem is soldered on
good, and use the brass stems as the chrome valve stems you have to grind the chrome off before you can solder them, and don't forget you have too use flux for the solder.
but I do like the metro vac all of you posted and I think I am going too get one as with my cans I have too make a few trips too the garage.