Used cooking oil

The first thing to remember is not to smoke the oil. If you smoke it, it's burnt. Throw it out.

Second buy a pack of cheesecloth at the hardware or even Wal Mart has it. Let oil cool then strain through cheesecloth into container. I do this and add new to bring it back to a gallon. Which is the size of my container. Store in dark place.

A lot of time I'll cut up a potato into say quarters and cook it at the end of frying. It tends to absorb a lot of the flavors and cleans it up.