What’s the origin of "arkees", the Rhodesian word for school toilets?

At the very British-colonial Routledge primary school in Rhodesia (now Zimbabwe) in the 1950s we were given breaks to run off to the toilets or "arkees" (I am giving the word a phonetic spelling).

Later in life men from other Rhodesian towns told me the word was also used in their primary schools, but with unknown origin. In those days local teacher training was in one college where the word may have been introduced as a euphemism, although some teachers migrated from UK and South Africa.

I have also hypothesised that the word may have originated from an abbreviation of "restroom" in those days when keys were not plentiful and often hung on labelled boards under the watchful eye of a custodian ("R-keys"), from "Ah-keys" indicating relief, or perhaps from the Afrikaans baby word "Akkies" (poo or pooing).

Any thoughts before all Rhodesians, with the exception of ridgebacks, become extinct?

The word 'restroom' could be translated into Dutch as 'rust kamer', hence 'RK' or 'ArKay'. If so, it could come from the West Germanic 'Afrikaan' settlers. Linguee