alt Hacker NewsIt reminds me of the aquarium filter I had as a child in which a plastic grate was placed underneath the gravel and connected air bubblers would create enough of an upward water flow in the corners that anything on the gravel surface would gradually get pulled beneath the plastic grate.
This is still one of the best forms of aquarium filtration. It encourages beneficial bacteria to grow throughout the substrate and they do most of the work. The air bubblers have a bonus side effect of aerating the water for fish an bacteria alike.