Abstract: A float member is provided defining a hollow chamber therein and a vertically elongated conduit depends downwardly from the float member and includes an upper portion projecting upwardly and opening into the hollow chamber to a level above the liquid level on the exterior of the float member. Heating structure is provided within the chamber in good heat transfer relation with the upper portion thereof projecting into the hollow chamber and condenser structure is provided for condensing liquid vapors. In addition, vapor conveying structure is provided and communicates the interior of the chamber with the condenser structure for conveying hot liquid vapors from the chamber into the condenser structure for condensing therein.