The BOOSTER makes refilling empty markers quicker and easier.  Screw BOOSTER onto the Various Ink bottle.  For COPIC SKETCH remove medium broad nib, insert booster into marker barrel and squeeze ink bottle firmly.  For COPIC marker, with broad nib still in marker, insert booster into the broad nib side and squeeze bottle firmly.  

 

FILLING WITHOUT BOOSTER -- hold marker at 45 degree angle, carefully drip and dab ink from ink bottle onto the nib. 

 

Refill bottles are calibrated for easy refill measurement.  COPIC Marker holds up to 4cc, COPIC SKETCH holds up to 3cc, and COPIC WIDE holds up to 5cc.