500 gallons of avgas in a very old and used bladder in a very old and used DC-3 up in Northern BC Canada. The Captain and I were sitting up front with the windows open and both smoking cigarettes when the bladder started leaking real bad. We very carefully put the smokes out, turned off the nav lights cause the gas was pouring out of the tail cone and through the tail light. We landed a short time later and finished our smokes. We lost a couple hundred lbs of gas though.