It's not quite as involved as kermath's, but it does the job!
It's a small HDPE drum (I have a 15G and an 18G) that I made as a small upflow barrel filter (like for small koi ponds). From the tank, dirty water is pumped into PVC that goes up-and-over the side of the tank and spins into the bottom of the drum. From there, the water goes through my pads and bio-media to the top of the barrel, where it gets sucked back into the tank by a plastic elbow (still in the barrel, near the top). This elbow is connected to another elbow leading back into the tank by a bulkhead (adapters can be used, too); this second piece of piping ends beneath the water surface. The idea is that when the water on top gets sucked into the outflow, it does so in a way that "flushes" rather than "pours" back into the tank. The result is that tank-bound water is restricted to flowing on one side of the outflow pipe at all times, the result of which is oxygenation/agitation within the outflow and bubble-shooting once the water gets back into the tank.
Finally, since the filter is elevated, I installed a drain into the bottom that is opened/closed by a valve. That way, when I have to take out waste water, I don't lose any prime because I just re-close the valve and let the filter fill back up. I run these filters on both of my tanks, and they're crystal-clear with very little maintenance/PWC's. (I still change out a bucket or two of water weekly). I use the full-blown 55 gallon version on my 300 gallon stock tank, during the summer. During that time, mayflies colonize the media and eat the detritus in the pads as well as algae.
That probably helped very little, so I think I'll just post the link to the site I consulted with (sorry for advertising another forum!) Maybe some DIY members who like ponds could benefit from this.
http://www.thepondforum.com/showthread. ... ond-FilterP.S.: Sorry for the bunny trail, kermath!