I don't know if you've ever watched those Freeview documentaries on tv about the railways DD, but when the fitters are in the maintenance pit underneath railway carriages on one part of the underfloor there's a rectangular chute, with bits of mashed up toilet paper stuck like papier mache around it, and it's the lavatory discharge chute.
Obviously the fitters try to avoid that area, but the track laying gangs have to contend with the railway sleepers, and one side, which is stained, is universally known as 'the cess'. 🤢