The ones I’ve seen were drip systems into a normal wood stove.
Seemed to work quite well. Probably not the most environmentally friendly setup.
Around my parts some of the auto parts stores take used oil and antifreeze and the local transfer station takes it as well. Both free of charge. They claim to recycle it.
Only the transfer station takes used cooking oil and they keep it separate from the motor oil.
The landfill charges here and it has to be in a clear container. The auto stores dont take it. I've seen a few regular wood stoves where they added a gravity drip through copper tubing.
There are companies that make waste oil furnaces. This is the only way to properly burn large quantities of used oil. The burner has to have an air supply and external “lift” pump. Also the burners usually have a heater built into them to thin the oil before it gets to the nozzle. I have setup and installed more than a few and the two that come to mind are Lanair and Clean Burn. Lanair is a great company to deal with.