Don’t add anything new to your calendar, just add them and they can see it’s useless for the purpose they want. When they complain, mention the checkin system and that you need to be called. Or just a generic “School Visits” event that isn’t specific to each location.
Make sure you have other evidence you’re actually working. Make sure people see you at each location so you have witnesses if your boss complains.
There may be more caveats here :/
I don’t have tile in my bathroom and have a decent vent fan and dry air so I have never had any issues related to this.