That taste can have a lot of causes, even the smoke of the fuel you use,whiffing over the things you heat up, happened once to me, made me ill.
If there were still residue's of production methodes, it should be sufficient to clean it as you do with your houshold cutlery and dishes, and maybe once making a "brew" with baking soda, leave that boiling for a few minutes and then clean as regular.
after that it should be good to go, I think.
Why I am asking for the "original" version here? Because recently I bought another canteen which was advertised as original, and that thing had for sure the original price, but was as flimsy as a sandwich bag, but since we are so far from any reasonable town with a army shop, I need to order by internet, and then I can't touch or see for myself, and to sent it back was way more expensive as the canteen. therefore I like to ask for experiences and then take the original stuff, to be sure it's solid.