Sul tasto -
Unable to find anything that really demonstrates flautando as well as the Sul Tasto video above (there is a video but the person doing the video doesnt really play all that well).
With flautando, you play with the bow right on the edge of the finger board.
With Sul tasto, you play usually with the bow anywhere from 20,30% up the fingerboard (split the fingerboard in four even quarters in your mind, put the bow about 25% up the fingerboard). HOWEVER, realize that Sul tasto CAN involve placing the bow ANYWHERE on the fingerboard (as long as it is not at the bottom, at the bottom it is specifically called flautando). In fact, one composer I know likes Sul tasto to be played with the bow ABOVE the fingers (up near the tuning knobs at the top of the instrument.
Flautando creates a flute like sound and should be played with a wide and fast bow movement, utlizing as much of the bow length as possible and a full stroke occuring every second to second and a half. It is often used to emulate the sound of a flute when flutes are not available (we had one of our violinists play a flute solo when our flutist was a no show back in high school).
Sul tasto creates a more haunting and airy / ethereal sound and should be played with wide bow strokes but slightly slower than flautando, a stroke every 2 seconds or so.
With both techniques, it is important for bow movements between each stroke to be kept exceptionally smooth (more so that usual) such that the elbow should not move. If not, you will get a scratchy sound. It is harder to get a natural and smooth sound with both of these techniques because the string has less area to 'ring' or vibrate freely.
I hope this helps. Its probably more than you wanted to know about this...