I have a wood stove in my shop, and when it gets hot enough with a bit of wood, I have a system made from a piece of stainless steel 1/4:" tubing with a valve in the middle of the tube. There is a 1-gallon funnel hung from one of the steel girders, and the other end goes through a small hole, drilled in the side of the stove.
My used oil goes into the funnel, and drips as much as desired into the stove. Illegal as heck here, but it works!
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