The gasoline is leaking from the gas tank...?

Chevy S 10, Pickup, 1999, 6-cyl , 4.3 L. I got the truck few days ago, every things is working fine. But, when I go to the Gas station and start filling up the gas tank around 18 gallons (gas tank was almost empty), it filled up only 14 gallons and i noticed like gasoline leaking from the car on the ground. I checked it to find where the leak was coming from and I find, the leaking was from the rubber hose which is going from the gas tank and connecting with metall pipe right at the clamp. I don't know what to do with it. I all ready tried to tighten the clamp but it doesn't work. Any ideas ?