Fuel delivery issues

The fuel line to the tank should not hold pressure. The tank has many open vents and with the gas cap off an even larger one.
A slight restriction could be you pushing fuel out of the tube and back into the tank.

I would still pull the hose off at the tank and blow into theline at the fuel pump end. There should be basically no restriction once any fuel in the line is blowen out.

You know the fuel pump works and the lines to the carb and carb are working

As a final thing you could hook up a piece of hose to the tank end of the fuel line, put that into a can of gas and see if it runs. Then you have only the sender pickup to be the issue