Hot water by itself should be enough, though you may have to flush a couple more times. I used iso alcohol the first time I cleaned out a clearomizer (long before TW even stocked them) and it was not a pleasant experience. I thought I'd rinsed it out real good, even let it sit overnight and did a quick dry burn, but there was still a little alcohol in the wick . . . let's just say it made for a
very unpleasant vape

Since them, I've only used water to flush them with and that seems to work just fine