Cant put gas in new tank. Help

Bought 1969 dart recently. Previous owner put in new gas tank but never filled it. I just tried to put in gas from a gas can and wound up wearing most of it. I thought maybe the filler hose or tank was blocked so I took a straightened out coat hanger and put it all the way thru into the tank with no obstructions. So I looked online and started looking for a vent hose. There is no vent hose but there is a vent line on the filler pipe that goes down under the car but not hooked up to anything. I looked online and found many 1969 gas tanks that dont use vents. This tank has no vents in it. Why wont the car take in gas? Thanks for your help.