There is a good reason why this request is made of us commuters. It's because sometimes the water and associated waste efluent comes out of the train.
I realised this today because, as I was standing on platform 4 of Reading station, staring into space, my eyes came into focus on the track in front of me.
And what did I see? I beige / brown "jobbie". Just lying there on the track looking at me. I looked around and there was loo paper and other general nastiness. Surely a public health issue but I don't blame the platform staff for not doing anything about it. I mean, who wants to do that job, especially with an audience.
So, let this be a lesson to you. DO NOT FLUSH WHILST AT A STATION.