Power
If you're referring to the power to fight germs and keep work and school spaces tidy, sanitary, and safe, then you're probably the most powerful person in the building. Nobody can wield a mop like you.
However, when it comes to making decisions beyond which disinfectant to use, you won't really get a say. You're the top executive in the janitorial department—especially if you're head janitor—but you don't have power anywhere else.
What's a powerless janitor to do? Most opt for joining unions. While this won't give you the power to lord over the messy masses, it does allow you to fight for fair wages and benefits. When these needs aren't met, the end result is usually a strike. After a week or so of dirty hallways and smelly bathrooms, the power of the janitor starts to shine through.