I agree with ctaylor. Pulling the fuel pump relay and jumpering the 7&8 pins will tell you a lot more about the situation than you would expect. Another possible problem is with the relay itself. When your car sits for a while, corrosion could create enough of an open circuit on the likely broken solder joints to prevent the pump from running. When you added the fuel to the intake, the engine moved and could have closed the gap in the broken relay solder joints. While the engine is running, the joints could vibrate enough to intermittently close the gap and the subsequent arcing could remove some of the corrosion to allow the car to start fine the next several times.

My money is on the fuel pump relay. Do a search here. I have documented my problem and how to solder it back together in around 10 minutes.