We use to own a incinerator, but used natural gas. Then EPA cracked down in incineration so we got out of that business. But, the amount of annual testing was ridiculous. You had to have a scrubber that would specifically address the metals. Everything else, you had to keep it running at least 1200F in order to flash everything but the metals and retention times had to be at least 2-5 seconds before the exhaust would leave the incinerator. I seriously doubt these garage heaters and shop warmers are generating that kind of heat. But if used for private, non commercial use, legally, you can....it's kind of like why you can throw away hazardous materials in your trash can, but you can't if you own a business, consumer commodities. Before the EPA crackdown, I knew a bunch of "recyclers" would come to the businesses and collect the used oil, add diesel fuel to it to bring up the BTU's and thin it out some, and they'd turn around and sell if for 1-2 bucks a gallon. I know Safety Kleen recycles the used oil after cleaning it and then putting certain additives in it. I know, I see their 55 gallon drums all over the motorpools and they met military specs. One thing I use to do with used oil years ago while living in Tennessee, we'd use it for chainsaw lube. Yeah, it's a lot thinner, but you'd definitely have a well oiled chain. One thing you can do, just take it all to a oil changing place when they are closed, put the buckets right outside their door and they will take it. I believe most of those places get a couple of coins per gallon they sell to the recycler.