The floor tile in the shower has a white spot

Huhu Cillit Bängggg seems to have worked :cool: we even had it in the household

I have to try that with us as well: We still have white paint streaks on the grout in one place or another from cleaning/painting (DIY work). Despite intense efforts, they haven't gone away yet and catch my eye every time (especially when you know where to look). I should probably put a bucket of clear water next to it just to be safe so that I can dilute and wipe away the agent immediately after it has worked.

Answer see - there is no drain.
The siphon is also not deep (for a walk-in shower) - so you can get something like that out relatively easily.