An elongated, imperforate housing (2) has a slurry inlet port (5) at one end and a pulp discharge port (6) at the other end. A pressing section (2b) within the housing is in direct fluid communication with the inlet port, and extracts liquid from the slurry by passing the slurry through a first compression restriction (108) to produce a pressed pulp. An annular washing section (2c) within the housing is positioned immediately downstream of, and in direct fluid communication with, the first compression restriction. The washing section has radially inner (109) and outer (14) cylindrical walls defining an annular washing chamber (110) for decompressing, diluting, and washing the pressed pulp. The washing is accomplished by injecting a washing liquid into the washing chamber through the inner wall, and simultaneously through the outer wall while the mixture is agitated. A repressing section (2d) within the housing is in direct fluid communication with the washing section, for receiving the conveyed mixture. The repressing section extracts the washing liquid from the mixture by passing the mixture through a second compression restriction (115) to produce a repressed pulp, which is then discharged through the discharge port. In a preferred embodiment, an additional, final pressing section (2e) is located between the repressing section and the discharge port, the final pressing section having a perforated, substantially cylindrical inner wall (116) formed in the screw shaft (3) and a deflection ring (49) defining an outer wall spaced from the inner wall.
