Donate it to Kramerica Industries for testing purposes...
Jump to 5:34 in the video
[video=youtube_share;lLQ1I-AF-5g]http://youtu.be/lLQ1I-AF-5g?t=5m34s[/video]
Was free to drop off a couple oil changes worth at autozone or advance. Had to ask the guys at the counter and they led me to the back room with the big barrel I dumped it in.
Many auto repair shops/transmission shops, etc have waste oil furnaces and store waste oil in 500gal+ tanks. Take it to them and they will actually thank you for it! Make sure there is NO water in your waste oil.
I have taken mine to Autozone in the past. Now in our hangar, we have a couple of barrels where we dump oil from filter changes on the planes and is picked up on a schedule so I have a convenient way to dispose of it myself. I wish I had a diesel generator, I would save a few drums myself, filter it and mix with the fuel we sump off the planes during overnight checks.