How often should I run the Drum Clean cycle and how do I start it?

The Drum Clean cycle should be performed once every 40 washes with no detergent or bleach applied, and the drum must be empty. To run it, press Power to turn on the machine, turn the Cycle Selector to Drum Clean, then press and hold Start/Pause. The water temperature is set to 70°C and cannot be changed. (Pages 39, 47)