http://www.aquariumadvice.com/forums/f14/new-tank-161749-102.html#post1555788
Here is a link to the one I built to give you an idea. Hopefully it helps.
Yep. If your tank isnt drilled then you need the overflow box.
Gafi said:does the actualy sump pump do that?
Gafi said:what rubble are you using?
Gafi said:and I gather this is all DIY?
Gafi said:ok so that is in the second column space? or is it in the second and third space?....what is in the spaces following the sand? looks like a heater maybe?
Heater and allows the water to flow as needed. Plus keeps the water over the bio filter and allows it to filtrate without going straight thru.