The dirty wash cloth fell into the toilet.
This is the adjective form of 汚, which is dirty. This word is the adjective dirty, but you can also use it to say things like filthy, foul, or unclean.
The reading is different from the other kun'yomi readings you've learned so far with this word. It is きたない. Think of it like you're saying "来た、な", as in "it came, huh?" What came? A really dirty looking monster, and it's coming for you.