I'm not familiar with that specific skimmer, but I have a similar one in my 16g 'spare' tank. You want the bubbles to run close to the top of the cylinder inside the collection cup. If you run it real close to the top you'll get wet skimmate with is OK, especially if you are trying to really clean the water. Run the bubbles a bit lower in the cylinder and you'll get much drier skimmate, almost like a thick soft slim and you won't be getting quite as much cleaning of the water and you'll be emptying the collection cup less often.
Watch the level of the bubbles when you fed (really, after you fed) or anytime you add anything to the tank as the level may change. If it goes way up, you can overflow the collection cup fairly easily. Also the water level that the skimmer sits in is very important. If you have an ATO (Auto Top Off) the water level will be quite stable. Otherwise when it goes down due to evaporation, the skimmer will be less effective and when the water level goes higher (when you replace the evaporated water) the skimmer runs the rise of over flowing the collection cup.