British cockney rhyming slang for a Yank (a Yankee, an American). As in 'Septic Tank Yank'. I'm told by my
British friends the origin of this was the
British military, where in WWI American infantrymen exhibited the worst of the worst language, and talked a lot of crap. But being from California, I remind them that I'm about as Yankee as an Australian is a Brit. Calling everyone in America a Yank is really ignorant. The British say Septic, while Australians generally say Seppo (compounded ignorance).