I'll take some pics to show you what I did and try to explain. I have an external pump (all the parts are what I could scrounge up around my house, my hubbys a plumber) I have a bio sponge on the base of the 3/4 PVC
pipe inside my tank for the intake. Then it comes up and outside the tank down under the stand through a shut off valve (which I also use to regulate flow) into the pump than into the first canister followed by the second. Through another shut off valve, up the backside of the tank and into the top for out put.
If I was to do it over again I would change the pump and try a submersible, priming this set up was a pain! Lol