Many years ago in the infancy of "The Home Shop Machinist" there was a recipe for soluble oil. I don't remember the proportions, but essentially you made up a fairly concentrated detergent solution and slowly added the oil to it. The other way around didn't work. If you added the detergent to the oil it wouldn't mix. I tried it and it worked OK. Easier to just buy the stuff today.
I had seen a way to cleanse used motor oil somewhere on the web. You needed two jugs, a thick rope and something to set the one jug higher than the other. It was like a siphon. You dipped the rope in the dirty oil jug, which was higher than the empty jug, and put the other end of the rope in the clean jug, supporting the rope in the middle with something so it didn't touch the sides of either jug. Wait 6 months until the oil wicks into the lower jug, cleaned of impurities by the rope and settling in the higher jug. I didn't try this one. I'd be interested in knowing if it works from someone who may have tried it.
RWL