The plunger is spring-loaded and will rise above the bottle by roughly 5″.  To keep the bottle from overflowing when putting the pump into the bottle, either pour a little chai out of the bottle first or pump mix into the pump as you insert it into the bottle as described below:

• First install the pump extension firmly into the bottom of the pump so it will reach to the bottom of the bottle.
• Make sure the top half of the pump is securely screwed onto the pump body.
• Then as you insert it into the bottle, pump it as you put it into the bottle.  This will fill the pump with chai and keep the liquid in the bottle from overflowing.
• Screw the pump onto the top of the bottle.

If you find the pump unsuitable, consider switching to a jigger for portioning.