A conventional liquid spray gun having a compressed air supply equipped with a liquid, e.g. paint, container for supplying the liquid to be sprayed onto a target surface. The container has a closed bottom, an open top and a cylindrical sidewall. A removable cover is attached over the open top of the container, and the cover has a pair of apertures extending through it, one of which holds a proximal end of a rigid tube whose distal end extends to a point close to the container's bottom. Slidingly mounted on the rigid tube is a generally circular, movable plunger whose periphery engages the cylindrical sidewall of the container. Pressurized air injected through the second aperture in the cover forces the plunger against the liquid's surface and causes the liquid to flow through the lumen of the rigid tube to the liquid inlet port of the spray gun.