The magnet is shown in the center (3), fully enclosed by the Archimedes screw (2).
The fluid enters at A and spirals around the magnet (blue arrows) upward to outlet B, bringing every particle within the magnetic field for at least 2 seconds.
The rotation of the magnet, in combination with the Archimedes screw, creates a screw conveyor which continuously transports the particles on the surface of the magnet to the bottom end where they fall into the collection chamber.
A sensor detects when the sludge chamber is full and starts the sludge discharge sequence.
The above diagram shows the operating principle: