Provided is an apparatus for processing a photographic sheet (9) which comprises at least one station (4) with inlet and outlet pressure roller pairs (42 to 45) for transporting the sheet, spray means (22) for spraying processing liquid (21) onto at least one surface of the sheet, characterised in that the station (4) comprises sealing means for maintaining a liquid seal (58, 59) between at least one roller of at least one roller pair and an adjacent wall of the washing station. Also provided is an apparatus for making an offset printing plate according to the silver salt diffusion transfer process, using the described station (4) as washing station. Also provided is a method for making an offset printing plate using the above described apparatus for processing an imaging element.