Want to provide a nice hideout for the eels in your aquarium? Try burying varying lengths of PVC under the rocks and sand, making sure the openings are easily accessible and free from sand and other debris. The eels will climb in and out of the pipes, allowing them to hide safely without running the risks of knocking over rocks or hurting themselves on the sharp rocks. Other fish and invertebrates might also take advantage of the tunnels, as the structures can provide instant hiding spots for a whole slew of different critters. If you decide to use these tunnels, be sure to clean them out on occasion. Just take a powerhead and blow through the pipes to remove sand and trapped detritus.