I do not know the origin of the ballad from which these lines are taken: it was reported to me from Sydney, Australia.
A song sung by Australian troops during the Gallipoli campaign of World War I. A fuller rendition is:
O the moon shone bright on Mrs. Porter
And on the daughter
of Mrs. Porter.
They wash their feet in soda water
and so they ougther
To keep them clean
Mrs. Porter was a madame of a Cairo brothel and she and her daughter were well known to Australian troops who created new (risque) lyrics to a popular ragtime song.
For those who wish to find the music with which to sing this passage Southam notes that the music is from the chorus of the ragtime song Red Wing by Thurland Chattaway.