Learn English – etymology of the term “right up the Wazoo”

Both up and out can be used in conjunction with the wazoo, and both imply too much of something. In this context, the wazoo is a slang term for the anus. The etymology of the term is uncertain. I have always felt that up the wazoo implied a more unpleasant situation than out the wazoo, but I'm sure that is simply a matter of personal preference. [cough].

Wiktionary has identical definitions for each term, and also makes note of the similarity to the phrase up/out the ying-yang [sic].

up the wazoo
1. (vulgar, idiomatic) up the ass; excessive or excessively; too much
e.g.: I'd go, but I'm sure they will charge up the wazoo for tickets.

out the wazoo
1. (vulgar, idiomatic) out the ass; excessive or excessively; too much
e.g.: I planted a few seeds and had radishes out the wazoo within a month.

An article in the Columbia Journalism Review provides some possible explanations for the origin of both the phrase and the word itself:

... the venerable Oxford English Dictionary weighs in. While it professes not to know the origin of “wazoo,” it says that others suspect it may come from the French oiseau, or bird, through a Louisiana Creole term, “razoo,” for raspberry. (Those with particularly fertile dirty minds may be able to make the connection.) It’s almost exclusively American.

The OED’s first two citations are telling in themselves. The first, in 1961, is from a University of California, Berkeley publication: “Run it up yer ol’ wazoo!” Its second citation is from a publication not known for its use of slang, The Wall Street Journal, in 1971: “Golf itself is quite safe, the greatest risk being the possibility of a long drive plunking some poor fellow in the wazoo.”

A post on grammarphobia.com mentions another possibility:

The Cassell’s Dictionary of Slang suggests that “wazoo” as a euphemism might be a variation on “gazoo” and “kazoo,” which had been put to similar uses in the 1960s. The OED also notes the similarities between the terms, and has citations for this slang usage of both “gazoo” (1965) and “kazoo” (1973).

Wikipedia offers a different explanation but, sadly, offers no reference or citation of any kind:

Slang for anus Originally derived from the Pama-Nyungan languages (the family of Indigenous Australian languages), and thought to refer to the anus of an animal, particularly the kangaroo.