My tank is only around 175 litres or so but the filter I purchased (an Eheim Classic 2217 to be exact – I was offered a great deal on it) filters around 1000 litres an hour.
Unsurprisingly, there are two hoses: one in and one out. These connect to the top and bottom of a large canister that has a strong pump sat on top of a set of filters (sponge filters in my case). The box did not seem to have all the bits required (or rather, a few too many bits, like four valve sections, but not enough extras to make it all usable) but we got it working. I had to prime it myself by sucking on the out pipe before shoving it into the spray-bar in the tank. Inevitably, after a few hearty sucks, I overdid things and ended up with a mouthful of fish tank water. Yuk. Still, shouldn’t harm me.
It was tricky getting the hoses connected up as the the tank is designed to fit in a corner and does so rather too well so access to the rear is very limited. I had to drop the hoses down the back from the top and waggle them around whilst my wife fished (pun intended) for them using a pair of cooking tongues through a small access whole in the back of the cabinet cupboard we were locating the filter in.
I still have the original filtering system in place, need to allow a while for a new bacterial culture to grow in the new system before I remove it. Having both in there (one being the built in system that sits above the tank) is a bit tricky and makes it difficult to close the top, which leaves things a little on the noisy side. I also worry a little about the simple suckers that hold the spray-bar in place because if they come loose and the hose comes out of the tank, we will virtually empty the tank onto the floor in about 20 minutes.
My daughter has several tanks with rather simpler internal filtering systems, but then she is around all week and relatively happy to do regular maintenance.
As a reminder to myself, my tank is an Aqua One UFO 700 Corner Aquarium and Cabinet, 175 litres, 108x71x55cm in silver with 3x20w fluorescent tubes. It has a built in filtration system.