A driver was doing maintenance on the gladhand connections on the front of a tank trailer. While climbing up to the catwalk area with a tire thumper and a razorblade knife (to rough up the rubber grommet to create a better seal), he fell. He landed on both feet on the fuel tank steps behind the cab. The tire thumper drove the pocketknife into his left little finger, causing a laceration near the first knuckle.