Have to admit I always thought spontaneous combustion was an urban myth (except in the case of the drummer from Spinal Tap)
But I always followed the rules anyways....pic attached is what if found left over of an old paint can with some oil soaked rags on it....set it on the shelf of my bbq to dry out. Note the gallon can was not squished down when I put it there.
Spontaneous Combustion.jpg