I dump drain oil in the tank for my furnace and burn it. Been doing it for years with no ill effects but don't try it with gear oil. Tranny fluid burns very well. Be sure you have plenty of heating oil in there when you do it and be sure you have a squeeky clean drain pan.

I learned all I need to know about life by killing smart people and eating their brains.
Eat right ,Exercise ,Stay fit, Die Anyway!