You guys do know those little 196cc China diesel engines will run fine on used motor oil? (Yes you'll need to filter it and remove any water before dumping it in the tank) They're horizontal shaft engines and can be mounted to garden tillers, go karts, mini bikes etc. If you can find one of the old Wheel Horse tractors I'm certain the little diesel would run a 32" mowing deck, maybe a bit more. Or possibly combine it with a cheap alternator to charge batteries for use with an off grid battery bank. Add a grid tie inverter and run the power back thru your meter etc? You're only limited by your imagination. Of course you could give away your used oil like most people do. There's always a free 55 gallon drum or two available in my area and I'm fairly rural here.