Merc 9.9 stopped running while running at trolling speeds (gas starvation..

We have a 2007 Merc 9.9 we use as a trolling motor on a 23-foot Penn Yan. We were trolling about 2.2 mph this past weekend when the motor stopped like it had run of gas. The gas tank was/is nearly 3/4 full but the tank pressure relief valve was tightly closed. After some trouble shooting, we found the fuel line was empty. We tested the hose to find bulb pump were full and under pressure. We connected the line to connector (Part no> 157871a) on the motor casing but could not get gasoline through the connector. Hence, there was not fuel in the filter. The connector looks pretty straight forward. What is inside the connector which could prevent fuel flow? Any and all suggestions greatly appreciated.

Thanks for the prompt response and suggestions. We tested the primer bulb on the gas hose and got good gas flow with plenty of pressure. I believe the hose connector was pushed all the way the casing-mounted connector since we had no leaks when we hooked the tank to the motor. The "o-ring" idea is one we hadn't explored since we were unsure of the inner workings of the connector. There appears to be some type of a backflow preventer in the motor casing-mounted connector. We pressed the steel pin on input of the casing-mounted connection and got some (a several drops) fuel (backflow at the input). It seems some of the fuel is going into the casing-mounted connecter but nothing is coming out. Would it make sense to insert a small metal pin into the output side of the casing-mounted connector to see of something is blocking the output hole?