This is in fact almost impossible. You can let it run out, but the container never dries out and it then rusts at one end. But to be honest, this "wet rag retraction function" is no good anyway and can only be understood as a marketing claim, it definitely doesn't make sense. If you want to mop, then you need one that washes out the cloths in between and dries them at the end, everything else is "window dressing".
Nevertheless, I can highly recommend the vacuum cleaner as a vacuum cleaner.

If you hold the water container with the opening facing downwards and shake it several times, almost all the water will come out, then leave it open to dry.

Hello unfortunately I don't know either I don't use the vacuum cleaner with the damp mop function and only use it as a vacuum cleaner and go straight after it with a damp mop, so I get a great clean result

I haven't had any rust in the water tank so far. I would pour out the water as best as possible and leave it open to dry, possibly in the sun.