The Quick Disconnect (QD) unit contains the integrated inlet/outlet system for the filter. The unit is removed by lifting the handle which releases the connection to the filter and shuts off flow from the aquarium. The mechanical parts on the inside are not serviceable so if the unit breaks during the warranty period consider contacting the manufacturer for a warranty replacement. After the warranty period you will need to purchase a new QD if the unit breaks. The unit also has two orings on the intake and discharge extension which do wear out and should be replaced if you notice water leaking from the cord area on the top of the motor. Replace the entire QD unit only if mechanically broken i.e. leaks more than a few drops after removal from the aquarium, water leaking from the QD area or the swivel joints of the intake and discharge tubes during filter operation.