It's usually scams for motor vehicles that the bait in these scams: in one morning alone, we heard from three buyers who had each lost over £6k paying unseen for non-existent cars.
Regrettably, I fear you have been the victim of a similar fraud, although by "tanker" I think you're referring to a farm trailer? If so, the irony is that unlike a motor vehicle this would have been covered by eBay's money back guarantee if only you had read the terms and conditions, and paid by Paypal. Paying by bank transfer removes any buyer protection.
I doubt there's much you can do now. Clearly you have to inform your bank, and the police, but if the bank transfer was successful your money could be anywhere in the world now. This is unlikely to be an amateur theft. This sounds like an extension of the endless motor vehicle scams on eBay, many of which the police have stated (to the scale of "multiple hundreds of false and fraudulent accounts) are the work of organised crime.
Good luck, but I'm afraid you may have to expect the worst.
