A VERTICALLY COLLAPSIBLE PRODUCT-ISOLATING SACK HAVING A REDUCED NECK PORTION AT ITS TOP, THROUGH WHICH THE PRODUCE PASSES, AND HAVING BELOW SAID NECK PORTION AN EXTERNALLY GROOVED ANNULAR SHOULDER ADAPTED TO FIT WITHIN THE TOP SHOULDER OF THE DISPENSER CASING AND TO PROVIDE PASSAGES WITHIN THE CASING SHOULDER FOR THE CHARGING OF THE CASING WITH PROPELLANT LIQUID. DURING SAID CHARGING THE ACK NECK IS SUPPORTED ABOVE THE CASING NECK AND IS SPACED RELATION THERETO, AND THE PROPELLANT LIQUID PASSES THROUGH THE EXISTING SPACE BETWEEN THE NECKS AND THROUGH THE GROOVES OF THE SACK SHOULDER, BEING BROUGHT INTO THE CASING.