Why does my new ECHO® product smell like fuel/have residue inside the fuel tank?

As part of the testing/assembly process, all engines are tested prior to leaving the factory. All units are tested by attaching lines directly to the carburetor and proper adjustments are made. For these units, there is no fuel/oil mixture that is added to the fuel tank. It is possible that certain batches of units are selected for further testing. If so, the fuel tanks are filled with fuel/oil mixture and ran for testing. The fuel tank's get emptied out however, some fuel/oil residue can still be visible in the fuel tank and the fuel tank may have the odor of fuel.