They were actually really clean and I was de-labelling for consistency with the rest of my bottles.
I also put a screw in the end that's held by the chuck so it can get a good grip on it.
I also thought about running small zip ties through the holes. *shrug*
That theoretically should get the toughest stuff removed without scratching.
I also recommend putting the chuck on the lowest tension setting so that you don't somehow (murphy's law) manage to get an exploded bottle stuck in your hand.