You should ideally use different guns for different products. A primer gun should have a bigger fluid tip to get slit more product on.
Personally have 7 but it's my job so makes it worth my while.
I have the luxury of gun cleaners but if you can get some gun cleaner thinners it will help. About £30 for 25 litres. If you can strip it down with cap off, fluid tip off and needle out. Then leave it to sit in thinners with the gun fully submerged in a big jug. Leave it for a good 15 mins and then get a gun cleaning kit with brushes and get it in there. Then leave to sit in some clean thinners. Don't throw the thinners as can use it all again for 10 mins. Then take it all out. Reassemble and dry off.