The cleaning of the riser tube is accomplished by a brush like device that rotates within the collection cup, scrubbing the build up off of the inside of the riser tube. Following the brush-like device is a small jet of water that continues to clean the inside of the tube, providing a clean surface for the foam to work.
But are these expensive gadgets worth it? Like most of the claims in the aquarium world, the claims about the self cleaning heads are not scientifically verified. According to manufacturers and hobbyists who use these devices, skimmate production can be increased by up to 30%. This may in fact be true, but is that 30% worth spending over a thousand dollars on a new gadget? Obviously some people believe in these self cleaning heads enough to spend the money, but these products are clearly out of reach for a majority of aquarium hobbyists.
Below is a video courtesy of YouTube showing just how these devices work.