Where to dispose used motor oil?

Well, this may sound awful, but when I have used motor oil (usually from my lawn mowers as I take my vehicles into my Chevy dealer for service), I pour the oil on paper and firewood in my home outside fire ring (which is sitting on concrete). I then ignite it, let it burn everything to ashes. After the ashes cool, I scoop them up, bag them and put them in my dumpster for the trash truck to haul away. I live in the country and there's no restrictions about burning or having open fires. Also, any wooden items (from all the amounts of remodeling I do) gets burned outside. Nails, screws, whatever, is then scooped up with the ashes, bagged and put in the dumpster. Inside the house, in our fire place, I only burn wood. Nothing with metal parts, staples, screws, paint, varnish, or any kind of glue (like plywood). All of that is burned outside and scooped up. The ashes from the inside fireplace are scooped up in my fire bucket (when cooled), and I toss them into the field behind our house. That's call "pot ash" and its good fertilizer for the field. I suppose there's one advantage to living in the country.