The chain comes with the replacement filler cap. I know this because I had to buy one after the old chain snapped right off and the old filler cap went for new adventures on the bottom of the sea. So in hindsight I'd rather use some string. Probably more durable, and definitely easier to inspect for wear than the silly drain plug chain. It's attached deep inside the filler fitting, so you need to take the hose off to access it.