Definition:
"Septic Tank" is English rhyming slang for "Yank". A "Yank" being an American, after "Yankee" (US Civil War).
Usage:
Look at those septic tanks (Americans) in their huge yank tanks (cars)!
Explanation:
Old rhyming slang used in Britain, probably by Cockneys of London.
Trivia:
If you have a fun fact associated with this word/phrase include it here.
