Abstract: A level-sensitive system responsive to the level of liquid in a container is provided. A level-sensitive device, e.g. a gauge or pressure switch, is connected by a line to a lower portion of the container. Gas, specifically air, is supplied to the line under pressure sufficient to enable the gas to pass slowly into the container and to bubble upwardly, thereby keeping the liquid out of the line and away from the level-sensitive device. The flow of the gas is sufficiently slow that it does not affect the operation of the level-sensitive device. A liquid such as water also can be supplied to the line under pressure to flow into the container. The quantity of the water is also maintained small enough so as not to affect the operation of the level-sensitive device. The water is effective to prevent growth of fungus or the like in the liquid of the container which otherwise can form adjacent the line leading into the container and block the line after a period of time.