Dye only works in a running system, and it's premature for that.

I agree that releasing r22 is worse than releasing 134a, but I didn't make the rules. The EPA does not allow release of 134a except for small bits required to purge the air from your hoses and fittings. However, release of the 4oz test charge of R22 is specifically allowed.

The real problem with moisture here will be that the oil is reactive with it. You really need to put oil in the compressor before you attach the lines.

I wouldn't recommend using air, but if you do, be aware that your airline water separator is not up to the job. Perhaps a desiccant dryer (as used for painting) would help enough.

As for evacuating a blend and recharging, unless you dump the charge out very fast you will probably remove very, very little oil. Is it legal to dispose of the blend in your backyard grill?