The cap of the Flexvent Top is conical in shape maximizing the clearance between the water level and venting valve. The venting valve forms an integral part of the cap so that it is impossible to damage the float vent mechanism from the outside. The large air cushion at the top of the Flexvent Top protects the valve seat against contamination, ensuring that the Flexvent will not leak. The air escape tube can be opened or closed with an adjustment screw.