i am a PPG certified painter. i probably spray automotive paint 5 times a week.
i use GRAVITY guns, cup above the spray gun. i also use disposable cup liners.
old style suction guns, cup below the gun. clean differently.

the shop had a spray gun cleaner. we use cheap wash thinner from the paint store in it.
we also have cheap thinner in a squeeze bottle for rinsing guns.

after painting i remove the cup.
i then use the bottle and spray about 1/2 oz of thinner in the cup adaptor. take a acid brush and stir the thinner a bit. then pull the trigger and let the thinner run out into the waste drum. i remove the air cap and then squeeze about 1/2 oz of thinner into the fluid tip to back flush the gun. i then put air cap and gun in gun cleaner. run for about 1 min. remove gun and blow dry outside and then thru the gun from the top and back thru the fluid tip. i then blow the air cap off and then use the squeeze bottle to force thinner thru every port in the cap., then blow dry. i then remove the needle and air cap, rinse them with thinner, blow dry. them rinse fluid openings in the gun with squeeze bottle. then blow dry. assemble gun and put away for next use. i use maybe 2 oz of thinner cleaning my gun.
after about 2 years doing this i replace the gun while it still sprays just fine.

i have 1 Sata 5000 digital WSP guns for water base coat. 1 Devilbiss Tekna gun for sealer and 1 Devilbiss Tekna for clear coat.


ultrasonic cleaners might work whit dirty DRY guns. i would just recommend stopping by harbour freight and buying their gun cleaning kit. it has wood tooth picks in it. use then to clean up dirt build up in the openings. this will be easier, faster and probably work better.