Hello !
The magnet is the original method of attachment of a tank to a Jobo processor. It is sitting at the bottom of the tank. The processor has a corresponding magnet coupling which is also used to drive the tank.
When you convert your processor to a lift, you remove the processor magnet and install a gear system to drive the tank. The tank is then put front first into the lift and when you lower the lift, it couple with the gear on the processor to rotate. The tank has, also to be converted to this use (I. E. have the corresponding gear on it's cover, be it from factory (reference # ending in 3) or added after sale (reference # ending in 1). In the later case, remove, if you can, the magnet to reduce the processors motor strain....
Hope this helps