New answers tagged propane
I'd use a pair of Tongue-and-groove pliers, just be careful not to crank too hard.
I'd be VERY careful about trying any sort of tool unless you are sure the tank is 100%, absolutely empty. The risk of shearing the valve off the top of the tank is nontrivial, and if there's any pressure that can be seriously dangerous. Personally I'd be inclined to drag the whole grill to someplace that sells tanks and see if you can persuade them to help ...
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