Abstract: In a pressure-fill container filling machine a vertical dispensing cylinder contains a piston that is forced upwardly by liquid product entering an inlet-outlet port in the bottom of the cylinder, the piston being forced downwardly by air pressure to expel the product from the volume chamber beneath the piston. The side of the cylinder at the upper end of the volume chamber is provided with a normally closed bleed passage for air. A tubular member extending downwardly from the inlet-outlet port has a lateral outlet opening connected by a by-pass passage with an inlet to the volume chamber spaced laterally from the inlet-outlet port. A check valve in the by-pass passage permits flow of liquid product therethrough under pressure from the tubular member only toward the volume chamber for flushing air out through the bleed passage while the piston is held in its lowest position.