I really dont dispose of my oil coolant just add to it as it gets low, no evaporation to speak of but I do throw some away in swarf.
I use old engine oil to get the fire going in the burn barrel and to spray my shed doors and wood fence ever so often, keeps them from rotting and the carpenter bees under control.
edit: my coolant concoction kills every bug that gets into the shop over night, thats a plus too, I leave the table led lights on 24 - 7 bugs go to the light an when they land on the table the show's over .