A cleaning apparatus for a radiation source assembly in a fluid treatment system, the cleaning system comprising: a cleaning carriage comprising a plurality of cleaning sleeves, each cleaning sleeve is configured to be engaged to an exterior of a radiation source assembly and each cleaning sleeve being moveable to remove fouling materials from an exterior portion of the radiation source assembly, each cleaning sleeve comprising at least one chamber for receiving a cleaning fluid and a cleaning sleeve inlet in fluid communication with the at least one chamber; a first conduit element for conveying the cleaning fluid to the cleaning sleeve inlet, the first conduit element being configured such that a distal portion of the first conduit element is in fluid communication with the cleaning sleeve inlet and a proximal portion of the first conduit element is disposed outside of fluid being treated in the fluid treatment system; a second conduit element for conveying cleaning fluid from a cleaning sleeve outlet in fluid communication with the at least one chamber, the second conduit element being configured such that a distal portion of the second conduit element is in fluid communication with the cleaning sleeve outlet and a proximal portion of the second conduit element is disposed outside of fluid being treated in the fluid treatment system; characterized in that: (i) the plurality of cleaning sleeves are connected serially in fluid communication with each other defining a cleaning fluid fill line in fluid communication with the first conduit element and (ii) the plurality of cleaning sleeves are connected serially in fluid communication with each other defining a cleaning fluid return line in fluid communication with the second conduit element. a cleaning carriage comprising a plurality of cleaning sleeves, each cleaning sleeve is configured to be engaged to an exterior of a radiation source assembly and each cleaning sleeve being moveable to remove fouling materials from an exterior portion of the radiation source assembly, each cleaning sleeve comprising at least one chamber for receiving a cleaning fluid and a cleaning sleeve inlet in fluid communication with the at least one chamber; a first conduit element for conveying the cleaning fluid to the cleaning sleeve inlet, the first conduit element being configured such that a distal portion of the first conduit element is in fluid communication with the cleaning sleeve inlet and a proximal portion of the first conduit element is disposed outside of fluid being treated in the fluid treatment system; a second conduit element for conveying cleaning fluid from a cleaning sleeve outlet in fluid communication with the at least one chamber, the second conduit element being configured such that a distal portion of the second conduit element is in fluid communication with the cleaning sleeve outlet and a proximal portion of the second conduit element is disposed outside of fluid being treated in the fluid treatment system; characterized in that: (i) the plurality of cleaning sleeves are connected serially in fluid communication with each other defining a cleaning fluid fill line in fluid communication with the first conduit element and (ii) the plurality of cleaning sleeves are connected serially in fluid communication with each other defining a cleaning fluid return line in fluid communication with the second conduit element.