Thanks everyone for your suggestions. I live in Europe, so couldn't find any "4 for $1" deals on eye-drop bottles. The only empty bottles that the pharmacy had for sale were big, heavy glass ones with fancy dropper-caps. I therefore just bought a plastic bottle full of eye drop liquid and cleaned it out. The top is easy to remove to refill it, and the hole needed just a little enlarging to make the rate of flow onto the chain ideal. It'll now live in my mini tool kit.