it's probably a homemade wet/dry sump that uses similar functions as those namebrand ones like the image. Here's a video, you get the idea. Only people with huge tanks, ponds, etc usually use these or something equivalent. On a smaller scale these are almost always seen with salt water setups or refugiums. There's a pet store here that has a homemade setup like I'm describing that feeds all of their freshwater tanks. Of course this isn't always the best idea if a fish gets sick.
THe pvc pipes that run along the top all get filtered through there before returning to the tanks
http://www.youtube.com/watch?v=ATzHjtFKMNs
THe pvc pipes that run along the top all get filtered through there before returning to the tanks
http://www.youtube.com/watch?v=ATzHjtFKMNs
