It's really straight-forward, Jeffy: internally, the commune adheres to the principles of communism -i.e. there is no need for, use of currency, everyone has skills they contribute to, jobs they do in support of the general welfare of the group, everyone is fed, etc.
For the commune's external dealings, as socio-political entities must necessarily engage in trade to procure the things they cannot produce internally, there is a general fund monetized in the coin of the hosting nation & comprised of earnings from the commune's communal output.
I fully expect you'll attempt to seize on the commune's external dealings with non-communist socio-political entities as an underpinning for your "A 'communist' commune in a capitalist country isn't actually communism" canard but keep in mind the dividing line between communism and capitalism is the difference between the internal and external. That said, let's see what you got.
Caption this Meme
