I'd like to learn the origin of the song, which I agree was a joke before it was a song. It's almost certainly not American in origin, since in America the word loo was not known, or at least wasn't used, until after World War II--and even since then it's been universally recognized as a Britishism. The word loo seems to have been known in Britain for a short time before WWII, and one theory is it was picked up by British soldiers during World War I as an abbreviation of the French phrase "lieux d'aisances" ("places of ease") which was used by the French as a euphemism for lavatory.

Since the Corries sang it, and with no evidence to the contrary, I (perhaps wrongly, but what the hey) assume it's Scottish in origin, in which case it may be the only Scottish song I feel comfortable singing in Scotland, since having lived in the Ozarks myself it's the only Scottish song that I can sing with a "native" accent better than the Scots can. ;-)