A cleaning system for cleaning gas paths in an engine core of a gas turbine engine includes a source of an engine cleaning liquid, an engine cleaning mist forming unit, a delivery device, a pump, and a mist collecting arrangement. The forming unit vapourises the cleaning liquid to form a cleaning mist and delivers the mist into the engine core. The delivery device delivers the cleaning liquid to the forming unit. The pump draws the mist through the engine core to clean the gas paths within the engine core. The mist collecting arrangement includes a condensing chamber, collects the mist that has passed through the engine core, and condenses the collected mist in the condensing chamber. The pump is arranged between and interconnects a rear engine core exhaust nozzle of the engine core and the condensing chamber.