Fuel pump advice.
 

The fuel pump in my 75, 280Sl with D-Jetronic seems to have failed. Car has sat for 6 months, and when attemting to check the injectors, prior to starting, found out no fuel was being delivered. We ended up removing the hose from the pump outlet to the filter, and applying 12 volts to the pump.
I could feel and hear the pump operating but no fuel came out of the pump.
We removed the infeed hose and there is plenty of fuel going into the pump
Sounds simple but heres the catch. The outlet fitting has a metallic something
in it. Logic says it is an anti-siphon device to keep fuel in the filter when the pump isn't running but in all my manuals and books I can find no mention of it.
Can't remove the fitting as all the fuel wants to pore out of the pump. If the pump is bad so be it. I hate to pay for a new one and find out it is just some operating principle I don't understand. Any assistance much appreciated.

although i am vague about specifics there is i beleive a check valve back there. perhaps it is stuck.

tom w