A system for a gauge well in a liquid storage tank with a floating roof including a floatable container located inside the gauge well and having a flexible laterally or radially serrated flange extending outward from the float and in contact with the inside of the well pipe to prevent vapor from the liquid stock from rising in the pipe. There may be a pair of such flexible flanges vertically spaced apart with the lower seal being just above the level of the liquid stock in the well pipe. A tape is attached at its lower end to a weight in the well pipe below the float and its upper end is connected to a winch outwardly of the upper end of the well pipe. A vertical passageway through the float is provided for the tape to pass freely therethrough and the float is freely slidable on the tape. The container includes a closed opening which is selectively opened to fill with the liquid stock at any selected level in the tank. The container also supports a thermometer and a D-ring member on top of the container to extract the float from the fill pipe when the tape is inadvertently broken.