1 or other of the 2 pumps should be working. Gravity feed would be enough to get main pump working but-
1. A small bore hose might cause the hose to collapse or the pump to cavitate, gravity feed in my 360 injection is 12mm (has a bottom outlet tank), 340 modifiers trying to pull fuel out the top of a tank from the 6mm outlet often have problems.
2. You need to prime the feed hose so it symphons the fuel from the jerry can, a pressure pump won't suck enough air to pull the fuel up out of the can.
3. If the pump is whining, it is usually working. It stops working because the brushes have worn out usually.
It seems to me your pressure pump test maybe flawed, and the lift pump in the tank is faulty. Disconnect the pressure pump power and listen for the lift pump working, and check it is definately getting power.
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