What is it when the fuel line that's in the tank of the 1989 Chevy caprice leaks in the tank before it even leaves the tank But the fuel pump works it just pumps fuel back in the tank?

Your pump hanger is a round plate with pressure and return lines plumbed through it and a bracket below, which supports the pump itself and the fuel level sender. Between the pump outlet and the outgoing pressure line is a short piece of joining hose. This can leak fuel from the pump directly back into the tank through cracks or loose clamps, lowering the line pressure. You'll have to remove the hanger/pump assembly from the tank to change it.