BigVV, I have a compost tumbler I hardly use (I prefer to use my big Rubbermaid compost bin since I cold compost, mainly for worms). How can you heat up used soil in it like you suggest? I thought the stuff you throw in the tumbler to make compost will heat up, but that is due to the compost forming. If you throw in just old potting soil by itself, I don't see how it will heat up...
Please give me more info, thanks.