Russell's Teapot

Russell's  teapot, along with the Flying Spaghetti Monster, is supposed to be very improbable in the absence of strong evidence that it does exist, and since we should consider the existence of a floating teapot to be highly improbable initially, we should reason in the same way for God. 

We do know that matter doesn't ordinarily arrange itself into the shape of a teapot unless there are persons around who want to heat and pour tea. How this is supposed to bear on the probability of something existing which , ex hypothesi, is not derived from natural processes, is something I don't understand.