Sewage dumped on tracks by trains is a 'health risk'
5 March 2014 Last updated at 15:17 GMT
Train companies have been accused of putting passengers' health at risk by dumping toilet waste on the tracks at some of London's mainline stations.
Modern trains are fitted with toilet tanks, which are pumped out at the depot when they become full, but older rolling stock does not have such a facility.
Unions say it is a health risk and companies should fit older trains with the tanks. The firms say the number of trains where this happens is decreasing.
BBC London's Transport Correspondent Tom Edwards spoke to Bob Crow, from the Rail, Maritime and Transport Workers' Union, and Seb Gordon, from the Rail Delivery Group.