Maybe try draining the tank into a can from each tap. If no fuel happens when you open the second of each taps, you were already on reserve, (or it's blocked).
Then as a check, pour the fuel back in, with a tap open, if fuel flows immediately, yer on reserve, if nothing flows, switch taps and see what happens.....if fuel flows, close it and open the other one and keep filling till fuel flows..and so forth...?? Trial and success-no errors here..??
I'm getting myself confused, but hope you get the drift.....??
While you doing this, beers are ok, but no smokin'......!!!