A fraud, a bluffer. To hold a four flush in poker is to have four cards of the same suit but not the fifth card that would make a potentially winning hand. Since four of a suit is worthless, a “four-flusher” is gambling that you'll believe her or she has the goods or the right stuff. The suggestion that a four-flusher is so full of crap that getting all of it down the toilet will take four pulls of the handle is an imaginative but incorrect derivation of the phrase.