Here! Let me google that for you
You'll end up with four sections.
1. Mechanical filter - Filter material can be bought in bulk for cheap. I use a thin coarse top layer so I can easily get rid of the majority of the waste buildup without having to clean the finer material that's underneath.
2. Biological filter - Bioballs (blah) or cheaper bulk material with more surface area (like shown in this picture http://z.about.com/d/saltaquarium/1/...lonefilter.jpg
, on the right). The water is sprinkled over this section of the filter (the "dry" part of the wet dry).
3. Sump - where your heater, pump, and bubble filter will be. The bubble filter is placed before the pump to prevent small bubbles from entering the pump, being chopped by the pump impeller, and getting back into your tank as micro bubbles (so small that they look like particles). Mine is set up so the biological material contacts the water at the bottom, so there's not enough perturbations at the surface to cause significant bubbles (plus, pump intake is at the bottom of the sump).
4. Overflow system - This gets your water into the filter. Ideally, you would drill a hole in the side of your tank, or you can use a siphon system, as I do, to get it over the edge of your tank. Google "DIY Siphon box". The concept is, you have your tank filled to a level where, if it goes any higher, it will overflow into the overflow box. This "overflowed" water drop down to the filter, then is pumped back into the tank, ad infinitum, or at least until enough water evaporates. I wish I could drill a hole in my tank...much less of a hassle. Edit: They sell overflow systems...I say get one...they're not that expensive and are fairly...involved.
I ended up making mine our of three stacked plastic containers. Top is filter material, middle is biological, bottom is sump (with pump and heater), all contained in a larger plastic container to protect the carpet.
Infinitely better than a powerfilter...you can really pack a lot of fine filter material in to get water that clears very quickly!
When buying a pump, just remember that the flow rate on the box is right out of the nozzle. You'll see a graph on the back showing the flow at different pump heights. I ended up with a 130GPH or something (can't remember) so I could get about 80GPH after the 4ft lift...short tank stand! You'll end up with something huge!