sump filter diy

I have unused 5 gallon tank and I wanted to try design the internal sump for it (Pandemic made me bored. I wanted to do some diy project.) I want my design to be on the side of the tank (like Fluval Spec 5...

Seen this online and wondered how efficient it would work.. seems like a genius set up.. I would use the first baffle to house a few tiny catfish to eat all the un eaten food from the display tank.. thanks for your opinions