I don't know that is available in Germany but, I would (if available,) double dose it with Star Tron. (Sta-bil, or similar.)
I would also run it with the above mix for a while before draining the tank.
Keep in mind, even if you empty the tank and 'run the system dry' you never really remove all of the fuel.
What you are trying to do is to prevent whatever fuel that is left from breaking down or, "going sour" as they used to say.
More than a few boaters after 'running dry', would remove the plugs and spray some moisture displacing lube/preservative into the cylinders and crank the motor a few revs before replacing the plugs. Of course, those motors were stored on or near the water.
Best of luck with your homecoming!
Cheers,
Smoketown