In addition to the dustbag, the vacuum cleaner contains two filters; a central filter that protects the motor and an electrostatic, "Clean Air" filter that removes particles from the exhausted air.
The Clean Air filter should be changed every six months or whenever it becomes dirty.
The central filter should be changed or rinsed out whenever the Clean Air filter is replaced.
Miele Air Clean Filter for Miele S175 Upright Vacuums.