If someone were to claim that there was a teapot orbiting the Sun between Earth and Mars, but this teapot was undetectable by any telescope, then we would react with incredulity. There is no evidence for such a teapot, so we would believe that there is no such teapot, and therefore we should believe that there is no God as there is no evidence for God.
The point of the argument is to show that lack of evidence for God entitles use to believe that that He doesn't exist.
Mark Sharlow in his new paperThe End of the Teapot Argument for Atheism (and All its Tawdry Imitators) quite rightly argues that these arguments are 'shockingly weak'. The reason that we react with disbelief is not because we lack evidence for such a teapot (because it's undetecable), but rather because such a teapot is intrinsically improbable. In order for a teapot to be orbiting the Sun between the Earth and Mars, humans would probably have to put it there. But we know that it's very unlikely that humans put a teapot there. The alternative is that the teapot formed by chance which is even more improbable. So belief in such teapot is implausible. Suppose that instead of a teapot, we are told that an oblong rock with 2 craters that is undetectable with telescopes is orbiting the Sun between Earth and Mars. Would we react with disbelief? No, because such an object isn't intrinsically improbable, eventhough it is undetectable and we have no evidence that such an object exists.
The difference between the oblong rock and the teapot is that we have independent reasons to doubt the existence of the latter. So in order for the teapot to be analogous to the existence of God, the athiest would have to present us with independent arguments against the existence of God. Without these arguments, the teapot argument is worthless. Suppose the athiest succeeds in presenting us arguments, the teapot argument would still be evidentially impotent, as any strength whatsoever that it has is solely from these independent arguments. Its the independent arguments that would be doing all of the work, so the teapot argument adds nothing to the atheist's case.
Sharlow goes through the variants of the teapot argument: the invisible pink unicorn, the flying spaghetti monster, faires, Santa etc. and shows that they are all likewise intrinsically improbable. He then offers another argument for the improbability of the orbiting teapot et al. based on arbitrariness. The moral is that if you want to argue that something doesn't exist then you need an argument. Appealing to orbiting teapots and invisible unicorns isn't going to help you.