A pump for a receptacle (10), in particular a bottle intended to contain a cosmetic product. The pump (1) has a pumping chamber (8) with a variable volume defined at least partly by a deformable membrane (3). The pump (1) functioning by varying the volume of the chamber (8) by elastic deformation of the membrane (3) between an initial state in which the chamber (8) has a maximum volume and a deformed state in which the volume of the chamber (8) is minimum. The chamber (8) being provided with an inlet orifice (22) and an outlet orifice for the product. The pump (1) has a means for deforming the membrane configured to exert a pressure on the membrane (3) and a guide rod (20) passing through the membrane (3). The membrane (3) slides along the rod (20) when it undergoes said deformation.