What kind of tool was it? Did it look like this?
What line are you having a problem with? Is it a rubber hose, metal line that uses that type fitting that that tool fits or just a regular flare fitting?
So what you are saying you are going to somehow have to fish out that broken piece of the tool from inside the fuel line fitting? Try a piece of mechanics wire or a cotter pin puller. Looks like this.
Inside the tank? Seems the only way to get that out would be to take the tank completely off the vehicle and turn it upside down. Do you need new clamps?
Seen here #14.
They have them here, too.