I watched the old man fill his grease gun for years, he always used a putty knife to load her full.
That is the best least messy way. I have had some real adventures over the years. Backing up 10 years, thinking all grease guns were much the same. Got a run of the mill gun. To fill pull the plunger back. Slip in the tube, release and go, looked good on paper.
Problem was with the spring cocked, I say cocked. Cause it is a grease hand grenade. The slightest bump caused it to release. No need to add to that picture, even if lucky enough to get the second tube loaded and top on.
The POS was a PIA to get primed. Never mind it oozed grease 24 x 7 x 365 as a constant reminder that's a POS/PIA.
As to priming, the cheap gun, after one gets the tube in. And having trouble getting it primed. Let it set in the sun, that softens the grease enough and allows the grease to push the air out that is in the top cap.
Finally solved all 3 problems buying a Lincoln gun
Hope you had a laugh, cause the grease hand grenade, is now funny looking back.
Pep