To improve sealing efficiency in a pump withdrawing liquid from a supply container (1) and to minimize the liquid residue in said container, the pump is designed to include a cylinder (5), a hollow plunger (6) configured within said cylinder, an external accessory pipe (7) configured at least partly within said plunger, and a feed pipe (8) configured at least partly within said external, accessory pipe, the internal feed pipe (8) being displaceable relative to the external accessory pipe (7) which in turn is displaceable relative to the hollow plunger (6).