Or, if you are really quick, you can try to fill the utube up perfectly full, cup your hands over both ends so no water leaks out, then put the utube in place and remove both hands at the exact same time to start the suction....
but trust me man, use the tubing and suck the air out... shove a couple of straws up there if you have no tubing... its just that much easier
remember as a kid, you used to attach several straws together to have this monstrous straw? You could drink your pop from the floor while sitting at the table...
Thats the image in my head when I recommended the straw thing