A plant container. Find one without drainage holes. Or make sure the holes are securely plugged because you don't want leaks. Don't use clay pots -- they're good at holding gardening soil, not water. If you use a ceramic pot, make sure it's fully glazed. I prefer plastic -- it's strong yet inexpensive. My pot is approximately 2 feet tall and 30 inches wide and holds 35 gallons of water.

An electric air pump, plastic tubing and combination foam filter and bubbler. All are available at reasonable prices at major pet stores. While it's possible to do without them, I don't advise it. A fetid mini-swamp isn't a lot of fun for you or your fish. Fish like the kind of oxygenation a bubbler provides.

Pebbles and cinder blocks. Rinse them off to make sure there's no harmful residue. The pebbles are for the bottom of the pot. One cinder block houses the electric pump, positioned next to the pot. Cover it with waterproof material, such as a garbage bag, to keep rain away from the pump. Use the other cinder block (or something similar) as a fish house. The fish will need a place to hide if cats or raccoons come prowling.