So far I only clean out the cup about every three days. I don't expect to clean the injector but once every three months or as needed.
From the manufacturer's directions:
The spray injector that powers your skimmer is designed to be maintenance free. In the unlikely event that a piece of algae or debris becomes clogged in the assembly, you can easily access the injector by unscrewing the small, white Injector Access Screw (see diagram below). Be sure and unplug the water pump before performing injector maintenance! Use a standard head screwdriver and remove the small screw by turning it counterclockwise – try not to let the screw fall into the skimmer once it is loose. Once removed, use the special injector brush to vigorouslyscrub the inside of the injector and spray port. IMPORTANT!! When replacing the Injector Access Screw DO NOT thread the screw so far that it will fall into the injector. Only thread it deep enough so that it seals the hole. It is normal for a small amount of water to drip out of the sealed hole during operation, and this shouldn’t be cause for concern. It is a good idea to remove and clean the water pump every 3-6 months to maintain optimum performance. Use an old toothbrush or scrub pad to remove any debris or calcium/salt deposits from the impeller and shaft.