A sump can be a fancy one like the one Blemmy_Guy is recomending, or it can just be a spare aquarium, or a rubbermaid container. Spare aquariums are easiest to modify, you can get glass or plexiglass squares from your local hardware store and silicone them in for any baffles or compartments you want. Rubbermaid containers are the cheapest option, $5-10 to add water volume to your aquarium and move equiptment out of sight without the fancy stuff.