The container, sump box of your skimmer will fulfill with all the organic waste and things it filter out of the water, so you should take off this container part and clean it more frequently to help clean the water better. It is easy to remove the skimmate with water then you can dry it and put the container back to your tank. Do this 3 times a week or with any schedule that fit the dirtying speed of the biological load. Generally, you need to clean protein skimmer every six months to maintain its quality and function. The air tube is hard to clean, as well as it will lose the quality after time, so you should better replace a new one instead of try to clean and reuse it after six months. Next thing to care about is the body of your skimmer. It will have microorganisms and algae sticking outside, which is quite hard to clean them up. You should take the body, remove all the water and suck it in a bucket with 5% vinegar water until the algae is easier to remove. After that, wipe down the dirt coat, wash it again with clean water and set up the skimmer body to your aquarium.