Going back about 5 years I was doing the windows at a mental hospital. Me and my mate were doing the georgeon windows inside that hadn't been cleaned for years, the water was coming off black, the bucket of water turned black after just a few windows.
We had to squeeze behind beds to get to the windows. Black drips on white pillows. We managed to accidentally do every pillow on the ward. The patents beds ended up dirty but at least the windows were clean. Then again it was a mental hospital so maybe nobody noticed.
Simon.