A vacuum pump comprises a casing having a bottom forming an aperture therein and a chamber slidably coupled within the casing. The chamber has a bottom forming an aperture therein. The vacuum pump further comprises a piston slidably coupled within the chamber. The piston includes an upper portion generally parallel to the chamber bottom. The piston further includes a hollow shaft extending from a bottom surface of the upper portion. The shaft has a first end adjacent to the upper portion and a second opposing end. The shaft is configured to fit within the chamber aperture and the casing aperture. The shaft includes at least one aperture positioned at the first end. The second end of the shaft is coupled to the casing at the casing aperture. The vacuum pump is configured to evacuate air from a flexible storage container by pushing the chamber in a downward direction.