Well.... however you can... You could use plexi and cut to fit. If you want to go super cheap, I might try getting another rubbermaid that fits in the bigger one. Use it as a baffle system. If you want the water to enter through the bottom, make the lip higer than water level then drill holes in the lower portion of the inner container. If you could find several containers that fit inside of each other, you could get several baffles going.