I've always found that gun cleaning was a PITA. I still have a 50+ year old suction feed gun that I painted my Model A and a couple other cars with, but don't use it at all anymore. My solution was a 3M Accuspray gun with their PPS system (disposable tips and cups) Current model. It cost me about $200, plus some additional for liners, etc. It cleans like a dream, and I'm still on my original 1.4 tip that I've used for primer on my current project so far. It takes about 3 ounces of solvent to clean the tip.
The production shops use a gun cleaning machine, but those are pretty much out of reach of the hobby painter. Paint gun cleaner
While looking that up, I also ran across this Gun cleaner spray that might be worth a try.

Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.