The screw screen is assembled directly in a waste water channel. The waste water flows through the screen basket that holds back the solids. While the waste water flows through the screen, the shaftless spiral conveys the solids upwards for dumping. During the conveying process, the inside of the screen will be continuously cleaned by special brushes attached onto the outer diameter of the spiral. If the screw is equipped with a drainage and compacting device, the screenings are drained and, depending on the material properties, educed by more than 35% of its own original volume.