An assembly for feeding liquid to the inlet port of a liquid spraying device or spray gun. The assembly includes a stiff container that defines an opening into a cavity in the container, and a flexible liner positioned within the cavity in the container has an outer surface generally corresponding in shape to the inner surface of the container, an inner surface defining a cavity in the liner, and an annular lip along the top end of the side wall defining an opening into the cavity in the liner. An included adapter assembly has a central portion with a through opening that is adapted to engage the inlet port of a liquid spraying device, a transverse portion including a peripheral part adapted for engagement within the flexible liner adjacent said top end of the container, and means for sealing the flexible liner around the peripheral part of the adapter assembly. An air supply assembly connected to the container supplies air at a relatively low pressure (e.g., in the range of about 0.5 to 8 pounds per square inch or 3.5 to 55 kilopascals) between the outer surface of the flexible liner and the inner surface of the container which improves the flow of liquids through the liquid spraying device or spray gun to which the assembly is attached, and allows that spraying device or spray gun to be used in any orientation.