1. Set a submersible pump in the bottom of the container. Using a pot that is at least 24 inches in diameter makes a splash and requires less water refilling than a smaller pot. Pull the pump electrical cord through the drainage hole of the pot.
2. Pull out enough cord to be able to connect to the outlet -- don't plug it in -- and leave sufficient slack to raise the pump in the pot. Close the drainage hole with premixed, quick-drying cement. Let the cement dry thoroughly; follow directions on the package.
3. Seal the inside of the pot -- whether it's terra-cotta, wood, or some other porous material -- with a liquid water sealant that is labeled for use on wood. Let the sealant dry completely.
4. Elevate the pump in the center of the container. Place it on bricks to bring it a few inches below where the water's surface will be. Fill the pot with water and connect the pump to the GFCI outlet. Be sure the water level does not dip below the pump.