A printer ROS window cleaning system enforces unidirectional cleaning motion through a passageway formed in the printer housing. A guide has a distal portion that engages a cleaning tool from insertion until a cleaning portion reaches the rear of the passageway. A cleaning tool deflector positioned at the rear of the passageway biases the cleaning tool from the distal portion of the passageway to a proximate portion so that the cleaning portion contacts the ROS window. A unidirectional cleaning feature ensures that the cleaning portion will contact the ROS window during removal of the cleaning tool by preventing re-insertion of the cleaning tool in the proximate portion of the passageway.