I've been taking my 300D drained oil to the local airport where they burn it in their hangar heater in the winter. The much cleaner drain oil from the Austin-Healey and the Toyota Tacoma gets blended in with diesel fuel in the 300D. I use from one to two quarts per tankful of diesel. Works fine. I don't think that 50/50 is necessary or even recommended. (Among other things, you would run out of drain oil way before the next oil change is due.)

Cheers,
Wes