Storing and re-using rendered duck fat
It's absolutely possible to re-use it, although you will want to keep an eye on how salty it gets as you use it for successive batches. It will also, like any fat, degrade as you repeatedly heat it up, so you can't keep it forever. It should be good for at least three rounds of duck confit, though.

Just strain it through some cheesecloth into a clean and dry container and store it anywhere it will stay solid, i.e., preferably the fridge (if you need the space in there a nice cool (&lt; 45˚F (7˚C)) and clean basement/larder will do).

Also, hang on to the jelly that ends up in the bottom -- it's like a salty aspic and makes a nice snack spread on toast, or diced up and tossed in a salad. You can also throw it into stews or make a sauce from it.