Apparatus, including an enclosure, a fluid-tight bag located within the enclosure, and a fluid-tight valve connected to the fluid-tight bag. The apparatus also has a tube, having a first end connected to the fluid-tight bag via the fluid-tight valve, and a second end connected to a balloon within a breast implant fitted to an implantee. The apparatus further includes a spindle, located within the enclosure, connected to the fluid-tight bag, and configured to rotate under control of the implantee so as to roll the fluid-tight bag onto the spindle or to unroll the fluid-tight bag from the spindle, and thus transfer a fluid, contained in the balloon, the tube, and the fluid-tight bag, therebetween.