The Bathmate penis pump is the world's first water-based device for enlarging the penis that gives instant sustainable results. It's a whole lot of fun too. The device is filled with water and placed over the penis, sealing at the base against your body. The Bathmate gaiter acts as both a seal and as the pump mechanism. As you compress the Bathmate device against your body, excess water is expelled causing a hydro vacuum which is much stronger than you could create with an air based vacuum pump.