basically get on all fours
Breathe out all your air, and suck your stomach in as hard as you can
do this for 3 sets of 3 reps of 10-15 seconds
A few guys on here tried them, and said they took about 3 inches off their waist... relaxed.
I guess it devlops the muscle that pulls your stomach in, and as a result of it being more devloped then before it constantly has a bit more tension on your stomach then usual.