For th historically minded, this song is based on the notices which used to be in toilets on BR trains until about 15-20 years ago. These said:

Please Refrain from Flushing the Toilet
While The Train is Standing in a Station.

The reason for this is that the toilets just chucked their contents out the bottom onto the track.

Oddly enough, the notices no longer appear, despite the fact that almost all train toilets continue to work in the same way. This leaves many English railway stations as essentially open sewers where the waiting passengers stare at piles of shit and chewed up toilet paper.

Not a pretty sight!

:-)