Fuel Pump Drain Hose Size?

The 912ULS installation manual shows the drainage hose for the mechanical fuel pump as 6mm "Outside Diameter" (see attachment) ...  Is this correct?  The diameter of the straight section of the hose barb on the fuel pump (after the lip) is 6mm....  I have some rubber hose that fits very well (tight) and it is 6mm "Inside Diameter"... I thought hoses were usually specified by the I.D.?  Comments?

Thanks,

Mike