Most of the people you meet on the cut are the sort of folk you are quite happy to share it with, but there are some idiots out there: See this recent advice from British Waterways:
Wheaton Aston Services closed Tuesday 4 January 2011 until further notice UPDATE (06 January 2011): Due to the misuse of the pump out facility by a customer to remove oil from a boat, this has damaged the pump out and drainage system. We are in the process of replacing the pump but this can't commence until Thursday 13th January. In the meantime the facility is closed except for water. British Waterways apologise for any inconvenience but we must stress that customers use the facility responsibly and within legislations.