84 Monte Carlo SS fuel problem

I need help, I am very stuck. I have a fuel problem and I can't figure it out. This car has a manual fuel pump drivin by a push rod from the engine. I have replaced the pump and check the push rod and still nothing comes out. I disconnected the two hoses comming from the gas tank and put my hoses stright fromt he pump to a can of gas, it worked like a charm. So I know my problem is from the lines back to the gas tank. Now the next step I did blew air back throught the lines to make sure they were not clogged. This was also ok, I think. So what could be the problem? Could the tank have big chunks of stuff blocking this lines, this is the only thing I have not checked yet.