I noticed that the gas won't come out of the tank once I pull off the fuel pump hose.  So, I went ahead and changed the tank for an other one.  Took me all day.  After finishing the job, I could not start the car.  Pulled off the hose and no gas from this tank either.  I just filled in five gallons.  So, blew in there, the gas started to come, the car started up, but soon it died.  
What is the reason?  Is there some valve inside to restrict the free flow?
Zoltan