The plumbing rod is a useful tool to add to you armory of weapons. Fish dont feed all the time but to learn more about the waters you fish and constantly get your baits to where the fish are can only improve your catch rate . You have to stalk them or bait them up with bread or corn, but you can catch them. If you see carp rooting around in shallow water, try to figure out what they are taking. Crayfish are often a good bet.
Carp are much smarter than trout, and can figure out a pattern quickly.
Then try and land the fly so that it sinks slowly within about 2 feet of the intended victim's nose. It seems that the carp will inhale the fly out curiosity providing it doesn't have to change direction to reach it. Surface flies generally don't work. The exceptions seem to be places where people regularly feed carp by tossing bread and the like into the water. Locate a fish and cast to it.