The AquaClear Extension Tube is a replacement or add-on part for the AquaClear Power Filter. Extension tubes play an important role in the filtration process， helping to filter out debris for a cleaner aquarium. Water is drawn into the extension tube， passes through to the motor and then gets pumped out of the impeller assembly. For deeper tanks， you can easily add more than one extension tube by nesting one inside the other and snapping them together.