[Tom Wesenberg]

What year car and what engine are you asking about?
From what's been said I'd assume it's a later car, such as in your avatar.

On later cars that may need a prime, I have used a rag around my blow gun and given the gas tank a few shots of compressed air. Go easy though, so you don't expand the tank. If the filler is in the open, in an emergency I have also used my mouth to blow air in, but I really don't like to do it this way.