Hebeanlage Sanivite Sanipump2 - How should it be cleaned?

We have a lifting system (Sanivite Sanipump2) in the utility room that pumps wastewater from the washing machine and sink upwards. This lifting system should be cleaned once a year; supposedly, it can be easily done by oneself, and there is no need to hire a craftsman. However, I can find no information on the internet about how to do this. Does anyone here perhaps have experience/tips? Thank you very much!

How expensive was this thing? I have here an almost 30-year-old lifting system from the hardware store, which has never been cleaned. And it doesn’t just lift a little wastewater...