The common name "pleco" is given to sucker-mouth catfish in the taxonomic family Loricariidae. There are several small and medium-sized species that can be kept in a home aquarium. The are called sucker-mouths because their mouths are shaped like suction cups and you will often catch them stuck to the side of your tank. Plecos are algae eaters, scouring the aquarium for any excess growth. They enjoy caves in their tanks, which they can retreat to if startled or use for breeding purposes.
Place a small clay flower pot on its side in your aquarium. Burrow the bottom part into the tank's substrate to hold it in place.
Place a piece of PVC pipe on its side in the tank. The piece should you big enough for the adult size of the pleco you're keeping. The fish should be able to turn around comfortably inside it. Size the PVC accordingly.
Stack pieces of aquarium-safe wood into a cave shape. Wood will give your tank a more natural look, if you're not partial to pots and pipe. Be sure your structure is arranged soundly and will not collapse. You can use aquarium-safe glue to hold the pieces of wood together.
Arrange pieces of slate and seal them together with aquarium-safe silicone. As with the wood, create a cave shape that will not fall and damage your fish or your tank. Stack smaller pieces of slate in parallel lines, gluing the pieces together, and then place a larger piece of slate on top to form a simple cave.
Add at least two caves to your tank for your plecos.
Adding any objects to a fully stocked and full tank will displace the water level. It is best to construct your caves when the tank is only half full or during initial set-up when the tank is completely empty. Do not place a pot, wood or slate cave in a bare-bottom tank. The material may cause damage. Place a substrate into the tank before adding a cave.