Firstly before anyone says so, that is not a jar of pee! It’s processed biodiesel!
This is the second of two posts on biodiesal, the first one showed how to make a cheap biodiesal processor and this one explains how to use the processor to produce biodiesel from waste cooking oil.
Years ago, restaurants etc were paying a fortune to have their waste oil disposed of; these days many have cottoned on to the fact that this waste oil can actually be valuable and they are now selling it so people can make biodiesel. That said, if you ask around and do some research you should still be able to find a supply of free or very cheap waste oil, especially if you have the capability to pick up and remove the oil from their premises.
(Photo from: drinkmorecoffee via Instructables)