The black plastic makes it practically invisible at the bottom of the pond. Bio-balls of various sizes are used in some aquarium filters. They are circular in shape and are made up of numerous tiny tubes at various angles to each other that form a large surface area. This filter system works both mechanically and biologically. Friendly bacteria called nitrifiers form a colony on the filtration media and process the toxic compounds, converting them to nitrates, which are used by pond plants as food.
Water is drawn from the pond into the filter unit.
Water leaves the pump through a rigid plastic tube connected to a fountain sprayer accessory or through a flexible hose connected to the outlet. The filtered water can be returned to the pond either way. I don't use the fountain sprayer because it tends to clog up with debris from all the plants and animals living in the pond. The flexible hose could be incorporated into a waterfall arrangement with a descending series of rocks. Ours is just submerged in the pond.