The Uli #3 is a method for gaining girth, particularly around the head. Basically, you get a partial erection , grab your penis with the OK grip a couple of inches behind the head, and trap blood between where your fingers are holding and the head of your penis. Then you pull toward the head, forcing the blood toward the head, engorging the area to the max.
There are many similar exercises being performed here. Most involve grabbing at the base , trapping as much blood as possible, and pulling forward, forcing it toward the head. Sizemeister's routine has some examples of some of these exercises.
The extreme ULI uses a clamp at the base of the penis to trap the blood. The clamp is tightened to prevent outflow and then to prevent both inflow and outflow of blood on a semi erect penis. Again this increases the pressure in the penis expanding the tissue.