I have three grease guns on the wall. One of them is for peculiar fittings that I don't even recall what they were on - something I no longer own, probably.
Last time I used one was at least two years ago and the last time I filled one was much longer back than that.
However, in the past my personal grease gun filling was from a small grease container that had a floating inner lid with a 1.5" hole in the middle so that allowed me to fill using the suction method. Unfortunately, so much time had elapsed since I last had to fill that way I made a complete pig's ear of it and grease got everywhere.
One of the other guns is a cartridge gun - much better.