How did “yazoo” come to mean “up the butt”, as “up the yazoo”. I know it is a river in Mississippi that runs into the Mississippi River, and that during the siege of Vicksburg the river played a role (e.g., Grant’s troops went “up the Yazoo” to attempt to attack Vicksburg from the east).
Now, “up the yazoo” means “abundant”, as in, “he has money up the yazoo”. I can’t find the origins of the slang use.
I concur on the idea that “wazoo” appears to be the common slang usage, with “kazoo”, “yazoo”, and “wazool” as variants.
Merriam-Webster says that its origin is unknown, dating it back to 1893, though another dictionary source claims it was not known until 1961. Wikipedia’s disambiguation page has this to say:
But no source is given for the claim, so it may be one with the dropbears in dry Aussie humour.