It has been reported that in some cases rats crawl up through toilet sewer pipes and emerge in the toilet bowl, so that toilet users may be at risk of having a rat crawl up their buttocks. Many rat exterminators do not believe this, as pipes, at generally six inches (15 centimeters) wide, are too large for rats to climb and are also very slippery. Reports by janitors are always on the top floor, and could involve the rats on the roof, entering the soil pipe through the roof vent, lowering themselves into the pipe and then into the toilet.