You would need the plumbing to go from your tank/overflow to connect to the top peice and a pump (submersible or inline) to run the water back into your tank. That fitting on the side is to go to a pump (in-line) or if its submersible you just put it in the final chamber and run piping from there. That side hole has removable plugs in it so you have an option of what you want to run.
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