I suppose you old timers already know this. I recently discovered how nicely paint can be handled when airbrushing by using a syringe. In my case I use a woodworker’s glue syringe. I use it to draw paint out of the bottle and also to draw up an appropriate amount of thinner. It’s easy to get the proportions right with the syringe. I then discharge the mixture into the paint cup, and draw it up again out of the cup once or twice which does a fine job of mixing the paint and solvent. Result? No more paint running down the side of the bottle, no spills while transferring to the cup, correct proportions of paint/solvent and well-mixed paint.
George