I would definitely take it back as a warranty issue.
Just in case you want to try this, here's a method that may clear the blockage. From a chemical/scientific supply house, obtain a rubber cork (one with a hole in the center) large enough to fit tightly in the filler neck. Drain the tank completely, turn off the petcock, and introduce some compressed air into the hole in the cork. The vent hole is the only escape avenue for the air so anything blocking it should be blown out.
