I built my own as well; below is the gist of the filter; it's a filter sock inside a 55 gallon drum. I was just telling Jamie about this, so pics were handy. I use this mech filter in conjunction with my bog (bog is secondary). I like this design as it's easy to clean (if I have to) by pulling the plastic cage+filter material out and hosing it off, but it didn't need it--lasted from February to the end of October, the whole season. Next spring, I'll just replace the filter material and sit back and enjoy another summer of no maintenance filtering.
The plastic chicken wire 'cage' is like an envelope (double-walled plastic chicken wire sewn with fishing line to form a cylinder) whereby I can slide the filter material in and out as necessary. This cage is shorter than the drum height, plus narrower than the drum diameter to allow for possible clogging without my awareness; the water will rise and spill over the cylindrical cage, then pass out the outlet if this happens. Normally, water will flow through the filter and clog, which makes the water rise more until new/clean material is encountered. Btw, I used (2) outlets (should have just done one at 3") as I figured out the outlet should be twice the diam of the inlet. In addition to the eco-felt fabric filter material, I lined the inside of the cage with window screen to catch any larger particles and extend the felt fabric's life.
