The drip tube is a long plastic pipe that extends from the top of the water heater down to near the bottom. Its primary function is to direct incoming cold water to the bottom of the tank, where it can be heated by the heating element. By directing the cold water to the bottom, the drip tube helps prevent the incoming cold water from mixing immediately with the hot water at the top. This separation minimizes heat loss and allows the heating element or burner to efficiently heat the cold water.