Then the Americans copied it and made a can that leaked (because it didn't have the recessed seam of the original) and needed tools (spanner and funnel) to fill.
The British had an early version that split in transport, punctured easily, leaked a quarter of the fuel they carried over rough roads and "gave vehicles a propensity to catch fire" (!) but when they saw the German design they immediately cottonned-on and made several improvements (cam lever cap release, air pocket and air pipe for smooth flow, gasket to leak-proof the mouth).
Finally, the Russians copied the German design, presumably without changes.
There is a deep lesson in all of this about the engineering practices, or perhaps the engineering traditions, of different nations. I'm sure there is.
I just can't get past the "gave vehicles a propensity to catch fire" bit.