MANY blue moons ago, I had a customer from Germany bring in tanks from Germany but without DOT markings, after research and checking, they could not be filled by any commercial operation in the US. If the customer had their own compressor, they can fill them. Hydro is an issue too according to the local hydro facilities (NY). In short, if not DOT stamped, no one in the US can fill them or approve of their use. The owner may fill them with their own compressor but any commercial operation won't/shouldn't. It also worth noting that all European made tanks sold in the US must have US DOT approval and markings even if they confirm to European standards. No one in their right mind would sell, fill, hydro or do anything with a tank that doesn't confirm to US DOT standards or doesn't have the DOT markings.
This was, as I said, long time ago and I am sure that the rules in the US have NOT changed.
