These are to be phased out, apparently. I was watching a documentary which said that disgusting piles of human effluent build up on the trackbed at London stations because people ignore the admonitions not to flush the toilets in station.
Such people were roundly lambasted inn the programme. If they are knowingly disregarding the warnings, then that is grossly inconsiderate I agree, but maybe - just maybe - they find it hard to believe that in 2018 trains actually still dump raw shite straight onto the railway? I found this incredible tbh. How much money do we spend on trains, and they can't fit a basic tank like a caravan has?