Set the absolute max price you would pay for it, and then offer 500 less. Negotiate without going over and don't be scared to walk away. If there isn't a big demand for tanks of this size, he will come down in price if he fears losing the sale. Only downside is that if someone else shows interest, you can lose the tank. But like someone mentioned, tell him you can have it out of there pronto and he doesn't have to worry about any of the moving except for moving your cold hard cash into his wallet, lol. Good Luck.