A slide up or down using the larynx is quite different from a gliss or fall using fingers moving down the scale (although the two can be somewhat combined).
I'm not sure which type of gliss Alexwan is referring to. If he means the typical fall down an octave or so, then the traditional way to do that is to slur down the chromatic scale. For an octave or more, I find it easier to use a scale in the key (major or minor), rather than the chromatic scale. For a shorter fall, the chromatic scale works pretty well. Either way you have to get the finger action very smooth. It helps to target a note and slide down to it, also dropping your volume and essentially fading out on the target note. It's hard to explain, and it takes some practice.