New fuel pump, new fuel filter. no fuel pressure.


I have a 2004 Mercury Grand marquis. 4.6l V8. Automatic. Just put new ELECTRICAL Fuel pump inside tank. and Fuel filter on. (not the whole pump assembly, Just the pump, clamps and rubber seal against tank) So anyway, when finished installing i double checked and made sure all of my lines were connected properly and gave them a tug to make sure they were fully connected. Now when turning key to " ON " position, i hear the pump buzzing near back seat versus the old pump did not.. so i primed it (turned key) 2 or 3 times and tried starting the car and of course its not starting. So i hooked up my compressor and attached the perfect rubber nozzle to shoot the gas lines with 20 psi of air... ( lines were disconnected from pump, fuel rail and filter). the low air pressure traveled effortlessly which tells my my fuel lines are relatively clean. the problem seems to originate from the very back fuel line where it comes out of the tank. So i assembled everything back together as if the job was complete, Except I left the very back fuel line " quick connect" Disconnected to see if i am getting any gas flow immediately from the tank. And as i guessed, no fuel came out of fuel line. To my Best knowledge, the main problem is taking place inside the tank where the pump is located on assembly... There is a black rubber hose(2-3 inches) going from the top of the pump and it leads to a white box. some people are telling me that this is the fuel pumps " Pulsator" others have told me it regulates pressure. Well this white box has an inlet hose connector and an outlet hose connector on opposing sides.(outlet connector leads straight to silver fuel line outside of fuel tank).. the white box also has a longer and thinner rubber tube connected that just leads down to the bottom of fuel tank ( air control? Gas return?) So the questions are obviously what else can i do to trouble shoot? what is this white box and why is no fuel passing through it to the other side?And what are the chances i bought a "new" bad pump? And lastly Would a low fuel level prevent the fuel pump from being able to pump fuel in the first place? Im currently sitting right under a quarter tank. Ive read that when installing a new pump, fuel tank should be filled to a minimum of half.... I am trying to avoid filling tank more in case the problem is elsewhere and i need to pull pump assembly again..If you need me to post pictures i can try to figure that out by logging in on my mobile phone. don't have pictures on computer but they are on my phone currently.

Thank you to anyone who took the time to read this extensive explanation and steps I've taken so far. Every comment and suggestion is very appreciated!!
And also Thanks to you Scotty! your videos are full of great information!