if it smells like paint thinner it may very well be contaminated with paint thinner!
i dont know about disposal issues there, but
around here if we have "any" thinner, brakefluid, chlorinated brake cleaner in a 55 gallon barell of waste oil
the drum becomes toxic waste and they charge 550 bucks to dispose of it!
so needless to say we don't allow anything in our waste oil stream.
i don't know about waste veggie, but i bet the guy you got that jug from has similar epa concerns, or if you are in
canada the canadian epa probably gets bitchy about thinners and such,
anyway i would not burn it in my engine even if it would run fine, it might offgas some sort of carcinagen and cause cancer.
same goes for a fireplace fuel, maybe more concern there.
i say take it back to the dude you got it from
bob g