The clear tube idea only really works for fish that use electric pulses to see, such as knifefish. Some fish, such as ghost knives, raphaels, and kuhlis are just naturally shy, and hardly ever come out of hiding during the day. For reclusive catfish, the best technique is to lean rocks against the front of the tank for the fish to hide under. Also, dimming the lights a touch might help them feel more secure.
Best of luck.