fill the 3gal up, pour it into the 5 gal, fill up the 3ga again, and fill up the 5gal exactly to the top, leaving 1 gal in the 3 gal, dump out the 5 gal, then pour the 1 gal into the 5 gal, fill up the gal again and pour in 3 more gals into the 5gal, leaving exactly 4 gallons!

I saw die hard with avengence......