Flush systems for flushing an object and flush toilets are disclosed. The flush system includes a first enclosed container for storing liquid to flush the object; a second container for filling liquid from a source; and a third enclosed container at least partially below each of the first enclosed container and the second container, the third enclosed container configured to contain liquid and gas and to be in fluid communication with each of the first enclosed container and the second container, and the first enclosed container and the second container configured to be in liquid communication via the third enclosed container. The gas in the third enclosed container is configured to exert a head pressure, via one or more conduits, to the liquid in the first enclosed container to flush the object.