VEVOR Pistol Grip Grease Gun, 3500 PSI, 4 OZ / 120 CC Capacity Heavy Duty Professional Grease Gun, with 11.65 Inch Flexible Hose 2 Black Flat Couplers, 1 Reinforced Nozzle, and 2 Rigid Metal Pipes

I asked this in my previous question, but it was not answered. I have had similar mini-grease guns. It is not clear whether the plunger rod is SUPPOSED to stay out after inserting the grease cartridge. Is it or should is slide back? Can you tell me? Should the rod go ALL THE WAY back in, THROUGH the grease, or does it go back as the grease is used up?