Klaus Raddatz's handy little tip deals with ready-to-spray Metalizers, but could just as easily be adapted to other paints:
"I use a Paasche Type H airbrush, with a paint cup. I never liked pouring ready-to-spray materials like Testor's Metalizer into the cup, then pouring the leftover material back into the jar; there's always a lot of waste. Simple solution: adapt the Metalizer bottle to the airbrush.
"I bought a small Paasche paint jar, and removed the fitting from the cap. Then I drilled a 1/4-inch hole in the center of an old Metalizer bottle cap, for the Paasche fitting. I assembled the fitting and washer to the cap, and drilled a 3/64" vent hole using the hole in the washer as a guide. Make sure you drill through the gasket too.
Measure and cut the Teflon tube that came with the Paasche jar to the correct length for the Metalizer jar. The tube should extend within 1/32 to 1/16 inch of the bottom.
"When I spray Metalizer, I simply screw the jar onto my airbrush, and spray whatever I need. When I'm done, I open the fluid tip all the way, unscrew the jar, and tap the Teflon pickup tube against the inside of the jar to drain the paint from the airbrush. Flush with a Metalizer jar full of thinner, and I'm ready for the next color.
"Cleanups are faster, with less waste, because there's only a small amount of residue inside the airbrush.
"An alternative to using old Metalizer jars is to purchase Model Master 1/2-ounce mixing bottles. It's the same jar and cap used for Metalizer."
Thanks, Klaus. Your visits to the Workshop are always informative.