My oil comes from the cafeteria at the hospital I work at and they change it once a week, about 8 gallons on average. The quality varies significantly. . . some weeks it's clean and clear, other weeks it's so fat-heavy it's a soft white solid at room temperature. It can be scooped with a spoon. Most of the time it's somewhere in between, it's a cloudy, thick liquid.
The solid stuff I put to the side and use in warmer weather. I've found if I take the heavy solid and heat it, put double the chemicals in and a cup of gas per 4 gallons and "cook" it for awhile, then mix with 50/50 clear veggie oil (heated & treated at the normal rate it) ends up almost 100% liquid and solid-free once cooled to room temperature. By the time it's mixed in the tank with a little gas and diesel it remains clear. So I've been able to make use of some pretty hard crisco. . . can hardly call it "veggie" since it's high in animal fat. . . kinda smells like chicken :-laf
I only use the crisco-quality stuff if I'm going to fill up right when I make it, that way it'll mix in good with the gas and diesel when I go to top it off. That's what I did today, mixed up some pretty heavy stuff and then after 12 gallons of the mix it took 3 gallons gas & 9 of diesel to fill up. Counting the chemicals I used for the process and the fillup costs it came to $55. It would have cost $94. 30 today if I filled with just diesel (paid $3. 92) so I saved almost 40 bucks with about 40 minutes' worth of effort.
Vaughn