OK, I will ignore blink's comments.
Seanw,
Now we know where you are coming from and your ability around engines, we know we are not trying to teach you to 'suck eggs' as the saying goes.
You will not get any appreciable fuel flow from the injector retun. That carries fuel which invariably leaks past the injector nozzle parts, as they are a close-tolerance metal to metal fit with no other means of sealing 'leak-by'.
The pump may only be a very low pressure device and the spring in the pump (to maintain cam contact) may disguise the difference between operation and non-operation. Also if there is air in the system you may well be simply compressing the air and not really moving any liquid. Lift pumps are generally reliable and long-lived and usually only need a new diapragm fitting - OK I have seen totalled ones but as I say generally....
Undo one of the bleed screws on the filter or injection pump and operate the lift pump to see if it is working. There may be something keeping one of the two non-return valves (in the lift pump) open, if sediment/foreign bodies from the tank has/have got into the line.
You will need to remove all air from the filter then the feed side of the Injection Pump (IP) and then make sure there is feed into the injector line from the IP. If air is present anywhere before or in the IP, it will not work properly.
Loosening the injector connector will then help to clear the high pressure lines of air while operating the IP. Finally when no air is being bled from the system , tightening the injector connection and operating the IP should enable you to hear the chracteristic 'creak' as the injector pops.
When at this point, you should be able to start the engine.
Regards, RAB