[After a brisk nap]

I never said they weren't (though as far as I can find, Scylla and Charybdis are only mentioned in passing, and never actually visited, in the Argonautica). My point was simply that the scene skizzy describes sounds like it's based on the Symplegades and how to pass through them in the story of Jason and the Argonauts, rather than on the episodes with Scylla and Charybdis in the Odyssey.

The Symplegades do not appear in the Odyssey, although a similar set of rocks, perhaps a related version of the same legend, known as the Planctae are mentioned (it's to avoid them that Odysseus passes between Scylla and Charybdis).