You do fill it between the chimney and tank after taking off the drip tip. When you want to open or close the juice flow, you need to slightly undo the drip tip so that the tank moves easier. Otherwise it is a ....* to try and turn the juice flow. I have the large tank and it still holds just over 4 mil which is pretty darn good for its size. One issue is that you are stuck with the small drip tip as it is needed to seal the tank. Works for me, I really like this setup.