Fill the flask up tipping a little bit to the one side so the water goes down the larger tube. Then when you go to pour out of that same side it will look like you dumped out all the water. Right the flask, and then when you pour again, more water will come out. You can repeat it several times before the reservoir is empty. I've seen similar at magic shops, but they require you plug a hole, this does not require any special hand placement. Only that you pour the correct way so you don't get water in the thinner u-tube meant to equalize the air pressure. Video: http://youtu.be/unbIjZYowtgWhen you print it, the top of the bottom reservoir gets a little goofed up, but it straightens itself out. I printed it with 10% fill and it works just fine. I'm sure it could have been designed better, but it is functional.