You can find a lot more helpful information elsewhere.
This discussion board has been active for nearly 5 years, during which time many topics have been discussed. Any question somebody may have has probably been addressed before.
My 3 has a 1.6d engine.I'm guessing it has the same size gasoline tank as yours (12g/55ltr).
When the final block on the fuel gauge burns out.It often has approximately 2/2.5 gallons remaining.Mazda's premise is that you don't have to worry about pulling dirt from the bottom of the tank.
I can drive mine for a week with the reading showing 0 range.