no more possibility to fill up with fresh water, to empty gray and black water.

asked if I could empty the cassette. the employee indicated that I could take in water with a minimum of € 50. The diesel price here was 7 cents more expensive so I went across the street at the mall, everything was free and diesel 7 cents cheaper

Seems you need to fill up with a minimum €50 of fuel before you get to use the services. Black waste in to the toilet, a drain to lift for grey waste and a tap available to fill up water.