oh boy ...
RU: Ja prodal jemu piesok.
Is this an expression in Polish?
Nothing idiomatic. "sprzedać piasek na pustyni" (to sell sand in the desert) is idiomatic.
Like in English "selling ice to an Eskimo"
The most popular English idiom would be "Selling, carrying, bringing, or taking coal(s) to Newcastle!" :)
Is there also the saying of carrying owls to Athens in England as well? At least we have it in German. :-)
"sprzedać lód eskimosom". Also works :)
or "eskimosowi" if you really want one Eskimo, but I prefer the plural version.
Or fridges; a common idiom in marketing.
I'd also mention "nosić drewno do lasu" (to carry wood to the forest).
Does the English sentence require "the sand" as I sold him sand would seem natural
No, it can also just be "sand" or "some sand".
some seems more likely than the