I agree, which is why I took an operatic vocal training class in college
- I highly recommend doing something like this.
It's a weird thing to describe; but I'll try in detail here:
First things first (and something I didn't really hint on in the last post); Jaw positioning: think of your inner mouth as an empty space that has a few objects here, there, a little bit of everywhere. Not only do you have a tongue that manipulates sound, but your ability to contort the empty space itself with your own jaw will change the pitch, timbre, and volume of the air that passes through the esophagus.
For "gurgly" shit there are a few ways and methods that can replicate the wet texture. One technique involves the tongue being placed at the tip of the bottom or top teeth with a slight curve along its body; lip positioning is important, but this is usually dependent on the structure of your jaw - so it would be a bit too hard to even explain - experiment with different shapes and angles (inwards, outwards, etc.)
Now, the throat itself is usually a little more constricted (I am not referring to your vocal chords, think more of the potion of your neck that is right where your jaw is above), and the constriction is important because it is used to force the exhaled/inhaled air into a pathway that will flow over your tongue and around the empty space in your mouth to create a sound. by altering the shape of this pathway, you are able to change the sonic texture and volume - but be warned, although all techniques can be applied to ex/inhaling, they are achieved differently (mainly due to tongue placement and breathe allotment).
Now, if you want the sewer sound without wetness (ala prostitute disfigurement) you basically force the air through smaller openings between your tongue and your mouth (most people do it with a tiny little 'o' on their lips, but it isn't necessary). The trick isn't just which portions are in the correct position though, it's the strength of the air flowing out of you. You don't have to push hard, but there better damn well be pressure - if done right you will not only have your normal overtone, but there will be a higher pitched undertone accompanying it.