A dip tube is a vertical pipe that extends from the top of a water heater to near the bottom. Its purpose is to draw water from near the top of the tank, where it is hottest. This helps to prevent sediment from building up at the bottom of the tank and ensures that hot water is available at the tap.
Over time, dip tubes can become clogged with sediment or scale. This can restrict the flow of water and reduce the efficiency of the water heater. Checking the dip tube regularly and cleaning it if necessary can help to prevent these problems.