I've used Unicolor kits. Yes, you pour the developer back into your container and re-use. About hrst's comment above: the Unicolor kits don't specify extending the dev time after each successive roll (or ever), but you'll still get good results. I've gotten around 14 rolls from a 1 L kit, but make sure you stash a few rolls to be developed so that you can do them mostly all at one time: once mixed, the chemicals only last about six weeks and I wouldn't even trust them for a month.