That would be like a control air tank and over time the air gets carried out with the water and you get waterlogged. If you had it capped on the top and a way to add some air from time to time a stand pipe would do a similar job. The units I showed have a piston in them and are charged with some preload pressure in the form of gas. Others have a spring and piston arrangement and others have a bladder. If I was going to make a DIY model I might get a couple caps and a big piece of pipe with a bung and stick a basketball inside.