Trouble with portable steel fuel tank

[fiftyfifty]

Just wondering if anyone can shed some light on why my metal tank (for a yamaha 90HP) has stopped allowing fuel to flow properly. The bulb remains pushed in after you squeeze it which sounds like a blockage somewhere. I have tried the following already:

replaced the primer bulb (thinking that one of the valves was faulty)
replaced the fuel hose and in-line filter (needed doing anyway)
unscrewed fuel gauge on tank and checked gauze at the base of the intake wasn't blocked. The remaining fuel trapped in the column under a vacuum drops out easy enough when you manually push the pin in on the fuel connector (next to the barb)
put a new fuel connector on the end of the fuel lineI have a newer plastic tank and it allows the fuel to flow without problem so I don't think there is a problem in the motor (e.g. fuel pump)

I also can't understand where the breather is on this type of tank. The plastic ones have the obvious breather you unscrew on the fuel cap.

Any suggestions would be appreciated. (I know the obvious solution is to get a new tank but it would be nice to solve the mystery!)

[tunaticer]

Wierd you haven't isolated the problem yet.

I doubt it be the breather as you have replaced the lines filters and bulb so the tank should not be negatively pressurised.

The primer bulb is the right way around?? Sounds silly but I have connected the entire fuel hose back to front once before not thinking clearly about the job. Can give this result.

With a gauze pickup filter it is highly unlikely to have a blockage unless it is internal corrosion in the metal pickup pipe, highly unlikely.

[finga]

The valves on the tank or on the female end of the fuel hose may not be pushing the little valve (barb) open in the connectors dodads??
If you want to try and resolve the breather theory just leave the cap off and try to prime up.