SCR system for treating the exhaust gases of an internal combustion engine, this system comprising a line for feeding a urea solution into the exhaust gases and a pump capable both of feeding the urea solution into the exhaust gases and of purging at least one part of the line by sucking a gas therethrough by means of a suction device, this system also comprising a control unit capable of activating and/or deactivating the operation of the pump and that of the suction device in a sequential manner in the course of one and the same purge procedure.