Abstract: A method and apparatus are proposed for cleaning the ink chamber (27) of the ink rail (11) of a printing machine ink supply system and from whch ink is delivered to an ink roller through a multiplicity of side-by-side stepped feed holes (29) in the rail (11) , the method and apparatus utilising a plug (41) freely slidable within the chamber (27) and adapted to purge the chamber (27) of ink present in advance of the plug (41) on its movement longitudinally of the chamber. In analogous manner the plug (41) may be used to effect a colour change as between ink sources provided at opposite ends of the rail. (FIG. 2).