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1.
Sepp, as in Septic Tank. Septic Tank is a cockney (East London) rhyming slang for Yank.
You dumb Sepp. = You dumb American.
by Commie April 06, 2004
 
2.
Young Aussie Trying really hard to be a Yank
A Western Australian term started in the year 2000 it can be Male or Female usually under the age of 29 years

They only need two of these to became a Sepp

The use of American Colloquialisms
dress like a American rapper, gangster or just simply wears American baseball hat backwards

Has NO respect towards their parents , Authority and
other.
They look at work has a Gaol sentences
They do not care about the Australian history
swearing in public, steeling, bashing and vandalism
Young Aussie Trying really hard to be a Yank (Sepps)
by George Copley June 07, 2010