I have a fungus in a toilet bowl. I drop bleach tabs in the tank, I pour bleach in the bowl, I scrub. No matter what I do... it comes back.
It has been there for years. This life form will not die. What if it mutates? What if it spreads? I wait for the day I read the words Resistance is futile written in fungus in the toilet bowl.
The "Theme from Jaws" plays in my head every time I enter that bathroom.