Just in case, he knocked on the door to the office before entering, but there was nobody there—only a desk, a few chairs, an empty filing cabinet, and a bookcase with a few volumes that were incomprehensible to a boy with only a week of magical education (and, in one case, because he couldn't read Latin). He'd been correct that the other room was a storeroom; it mainly seemed to contain anatomical dummies of various sorts covered in sheets, but more usefully, it included a mop and bucket. Harry left the mop in the classroom, then carried the bucket to a nearby loo and filled it with soap and water. Then he carried the bucket back to the classroom and got to work.