I used to work with the steam engines at Tyseley Musuem Depot near Birmingham in the 70s.
Some of the older chaps there used to sing this song.

The version they sung was:

While the train is in the station
please refrain from urination.
Have regard for railway property.
If you wish to pass on water
go and ask a railway porter
he'll direct you to the station lavatory.

.. didn't realise it was a well known ditty.
Could be they had misremembered it, or adapted it a bit.