Where to get rid of dirty oil?

I dont know about recycling of used oil

But down here we use the used motor oil on the wood decks of the wagon/trailers. We brush it on in the fall since they get stored outside during the snow days. We do not have enough indoor storage for the wagons/trailer.

Keeps the wood from rotting. The last trailer we had, the steel rusted away in 15 years but the wood looked like new.