Dont bother with the pump.. trust me..
Freeze the bottle overnight then fill from mother bottle...(i've seen guys use a cooler filled with Ice and watter for a quicker turn arround...just dunk bottle for 1/2 hr or so..(not quite as good as freezer but works well too)
Get mother bottle withOUT tube, invert entire bottle..(you'll get more liquid nitrous out this way..(be sure to use filter)
You should be able to easily fill to the max amount called for on the tank..(don't overfill)
Works great.