Watertight arguments of any sort are hard to come by - I have none of them, have heard none of them, and have my doubts about the claims of those who claim to have such. Every argument I have ever heard can be challenged sufficiently to throw some doubt on it.
But why is 'some doubt' the standard?
'Reasonable doubt' is a better alternative. Maybe even 'a preponderance of evidence'.
We don't acquit someone of murder because their lawyers argue that the twenty eye-witness accounts of them doing it, and the dozens of pieces of forensic evidence, could have been convincingly faked by a sufficiently powerful, but currently unknown, party or parties.
It's impossible to prove that the whole thing isn't a set up to frame the defendant; Yet despite this, murderers are routinely convicted by juries.
God claims are typically far less convincing than that pathetic travesty of a legal defence.
If something
could be true, but only if we discard General Relativity or Quantum Field Theory, then in sane layman's terms,
it's false.
No reasonable person accepts that Russell's Teapot exists. There's no evidence to support its existence, and for it to exist would require a lot of things that are very well established as almost certainly true, to in fact turn out to be false. Gods, as described by current Abrahamic sects, are less plausible than Russell's Teapot. They require contraventions of scientific law that the teapot does not.
You would be considered a nutter, if you appealed for others to at least respect the beliefs of those who think there really is a teapot orbiting somewhere in the asteroid belt. And yet appeals to respect the beliefs of those who think gods are real are somehow immune from ridicule.
But such appeals are ridiculous.
When the absolute BEST evidence for the existence of a hypothesised entity is "We cannot prove with complete certainty that it doesn't exist", the only sane provisional stance to take is "it doesn't exist". That's just as true of gods as it is of cosmic teapots.
Watertight arguments are an absurd and unreasonable standard. That gods do not exist is WAAAAAY beyond a reasonable doubt. That ought to be good enough for anyone with the slightest respect for reality.