I want to infuse my ACQ posts with used motor oil. To that end, I had planned on using a large pipe, filled with oil, and placing a post in it, pulling a vacuum for a day, then letting the post dry out.
Here in Florida, ACQ posts don't last anywhere near as long as the older "pressure treated" wood. The posts are set below the water level at least half the year. My older posts are still robust, but the ACQ ones are not holding up as well. With a good bit of erosion below the surface.
Might be a good use for old oil. Certainly, it's nasty enough to keep bugs and rot away.