>> This sentence is false, since you do not have any basis to refer to a vat.

I know what a vat is here in subjective world, I am able to imagine a situation in which such a thing exists somewhere with something like my perceived centre of consciousness within it being fed false data. Should that (or some other solipsistic scenario as yet unimagined) actually be the case I am fully aware I do not have the terms of reference to accurately describe the scenario as I have been relying on false data for my entire life. However an accurate description of the scenario is entirely unnecessary to the thought experiment itself and dismissing the entire argument based on the statement that we cannot properly describe a vat is to fail to address the root of the argument and attempt escape on a technicality.

Or, in other words, you could be a brain in a vat.