Since I live in Canada and we have some bitter cold days I find just leaving the cubes of oil outside will freze the water in the bottom and just pour off the oil .
I have did this in the past and the oil is VERY thick though .
I have been picking up used oil for years now and giving it to a group of people that feed bears and watch them. They pour the oil over the grain base feed
Recently dropped off some cubes and thought "" I SHOULD be useing this for fuel ""
Hence me joining this forum and trying to figure out what is needed ; and the cost and the troubles  and the space required ; involved  with using this type of fuel