Abstract: Waste washout liquid containing liquid washable photopolymer from a printing plate manufacturing process is subjected to filtration via a centrifugal filter unit. The unit has a collector for the solid material arranged for rotation and disposed so as to allow deposition upon it of solid material during its rotation. The unit is fitted with at least one of a pretreatment unit for coagulating the solid material and a collector removable from the filter unit so as to allow its disposal together with the solid material deposited on it. Usually, the pretreatment unit is a preheater and the collector is a disposable liner within a rotatable chamber.