Even though the center drain and external stand pipe removes a considerable amount of settleable solids, and allows me to not have to do a water change for 3 to 5 days, a mechanical filter is still needed to strain out the suspended solids in the water column.
The mechanical filter consists of a 55 gallon drum that is packed with almost one roll of deer fence garden netting available at most big box stores like Menards, and some filter pads from Stoney Creek Equipment Company.
Note the u-tube siphon in the tank that works by gravity. That is, it pulls water from the water column of the fish tank to the bottom of the 55 gallon drum under the netting and filter pads. It does this due to the fact that water is being pulled out of the top of the 55 gallon drum via a small pump.
The u-tube siphon and a couple of end caps.
It's primed by simply submerging it in the fish tank and temporarily capping the end that is lifted out of the fish tank into the 55 gallon drum. The will run indefinitely as long as both ends are under water.
Suspended particulate is trapped in the filter material as the water gets pulled up through it.
Every four or five days an extension of the u-tube siphon in the drum is removed and the siphon capped (see picture of u-tube siphon) and a drain is opened in a drain hose in the bottom of the tank. The pump is also temporarily hung in the fish tank and kept running.
Once the water is drained out of the drum the filter material is sprayed off with a garden hose and nozzle and placed temporarily in garbage can or other drum. The empty tank is scoured out with the garden hose and completely drained and then the ball valve in the drain hose is closed again.
Clean water is put into the drum, and the filter material and pump replaced as before.
