On both of mine, where the water enters the skimmer is a venturi, I thought they were all like this, there's an airline that runs down to a fitting. There's a thumb screw that you use to adjust the airflow through the airline.
To service the venturi, you unscrew the slip fitting from the skimmer, then use a butter knife to unscrew the venturi, it can get plugged up. You'll see two slots on the venturi fitting, it's a threaded plug with a taper. The airline enters the top right above the plug.
It's much better to use a good venturi, like the kent venturi instead of the stock one, just remove the stock one.
