Dip tube,,,Think like a straw in a cup of soda. You suck the soda through the straw thats end is very near the bottom of the cup. Essentially, a dip tube is going to work the same way, but instead of creating negative pressure at the outlest end of the straw, you would create positive pressure (more pressure than is at the open end of the straw) inside the cup, forcing the liquid out. This is how kegs work.
In the absence of a dip tube, by inverting (turning upside down) the container of co2, the the liquid co2 would be able to exit through the top of the container (which is now the bottom since you turned it upside down). Gravity keeps the liquid co2 in the bottom of the tank when it is upright (because liquid co2 is more dense "heavier" than co2 in a gas state), with a layer of gaseous co2 seperating the liquid co2 from the valve. Turning the container upside down will put the valve at the bottom of the tank, thereby exposing it to liquid co2. I would be very careful with this, as you can "freeze" the valve open and end up emptying the tank with possibly spectacular (but not necessarily good) side effects.
BTW, whatever liquid you are combining with the co2 is likely to be frozen as a result of what you describe. When the co2 converts to a gas from liquid, it is going to absorb heat energy, this absorbsion is going to be quite pronounced. Are you thinking about making a slushy machine with this?
Don't take this the wrong way, but I would strongly advise you to read up a little on thermodynamics in relation to liquid to gas conversion. By the wording of your questions, it sounds like there may be a couple of voids in your knowlege. You run a very high risk of injury if you are not careful.