Yeah, I hate my housemates ability to clean of something. If it was in this house, you clean it, show me and do it again. Till you've done it properly. I have all day to spare.
Same thing happened to me. My mom hired me to deep clean her office (I'm unemployed unfortunately) and after 2 hours of cleaning, when I moved to the room her office is in, she felt the need to start explaining in baby terms on how I should be cleaning. Wouldn't that have been helpful in the beginning as oppose to when I'm finished??
Keep telling your manager you don't quite understand and show you again and again on a new spot. Your manager would eventually clean the whole place up and you wouldn't even need to lift a finger!