How to clean water intake filter - Diplomat ADP 8242?

Fully integrated dishwasher professionally installed early 2003. Recently items no cleaner than when they were stacked, eg tea-stained mugs, almost as if not even switched on, although detergent dispensed and operation can be heard.

Naturally, have thoroughly cleaned machine but manual refers to cleaning the "water intake filter". However, there is no diagram to show where this is - could it be at the point where the hose joins the water pipe under the kitchen sink?

At this moment, am treating the m/c to a special cleansing treatment ("Finish" product) but if the problem is the filter I'd prefer to solve it if possible.

Grateful for any advice.