Nick wrote:

Does anyone know of an economical way of either using this waste for heating
purposes or a more economical method of disposal.

My mate's dad heats his workshop in winter with a purpose-built heater
running on waste oil. I believe it drips the oil onto a hot cast-iron
plate where it burns, inside a heavy iron casing. A fan blows air round
the outside of this casing and into the room. Lighting it is somewhat
involved; you have to stuff a few diesel-soaked rags into the bottom to
heat the plate up before it can start burning oil. Apparently though you
can buy self-starting versions, at a price.

He has a big tank outside (domestic heating oil tank surplus to
requirements) that slowly fills up over the summer and gets used during
winter.

Pete