I've got a few gallons of used oil in the hangar in buckets since I
don't drink enough milk to put it all out for recycling. One of
these days I need to schlep it over to the big oil recycling tank
at a nearby airport.

If those are polypropylene milk jugs, you don't want to leave them
sitting very long. Polypropylene absorbs oil and will disintegrate if
left in contact with each other. Don't leave the jugs on the hangar
floor unless you want to clean a gooey mess. Is your hangar floor
epoxied?