Sort of what my thought was. Given the skill of the previous owner and the smell of the stuff I'd bet there's already RUG in it.
I am picking up 50 gallons of fresh stuff next weekend at $1 a gallon so I'm not too worries about discarding 6-8 gallons of nasty stuff.
The main tank in the car is completely drained of old oil so I'm going to put a gallon of diesel or two in there and take a drive swirving about to slosh the diesel around and clean the gunk out of the tank. Then.....I get to sort through this stuff.
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