FILTER DESCRIPTON:
The body of the filter is a 55 gl. barrel. The media holder is a perforated wastebasket. It's held on place by a 1/2" PVC pipe with tread at both extremes and using a plasticd washer and nut: one under the basket and one over the tank cover.
The basket is filled with filtrer floss, and If needed, zeolit, carbon or whatever you need to put there. When water has been filtered, it splashed over the bio-ball (biological filtration / gas excahnge) and is then pumped back to the tank by the pump.
In the pipes, there are many valve balls and check valves that prevent the water from backsyphoning in case of a power failure.