How Do Self-Cleaning Pressurized Filters Work?

[Julles]

I am disappointed in my new Fish Mate pressurized filter, which is supposed to have an "E-Z Cleanse" feature, meaning you simply turn a knob and it's supposed to squeeze the gunk out of the foam core.  You attach a hose, and the sludgy water is forced out.

Well, not only does the filter leak, so I had to set IN my pond, instead of hiding it outside among the garden plants, but the cleaning feature simply doesn't work.

I took it apart, and don't see any aparatus that is capable of squeezing the foam core.  From what I can tell, all it does is force water into the bottom of the filter, where it has to pass through the foam block and then the bio balls, but there's not enough force to push out the fish poo stuck in the foam.

Does anyone have this sort of filter?  Can you explain how it's supposed to work?  I am thinking maybe I'm missing a part, although I had everything that was on the diagram sent with the instructions. 

I can't believe I spent $200 on something that won't do what it claims.