yep its completely impossible, not even close. then the apologists either say "its an allegory", or the literalists just stick their fingers in their ears or make stuff up.
But to be honest I pity them, for a believer the fear of hell is SO REAL. You telling them the flood is bs means one of 2 things:
either a) god doesnt exist, shattering their belief system, so they have been wasting their whole life, and risk losing friends and family OR
b) the flood is true, god is real, and you are trying to test their faith and get them sent to hell.
which is why skeptics/agnostic/atheists are so hated, and why i don't really bother engaging them.