The skimmer collection cup has to be emptied on a regular basis. Depending on how you have it adjusted, it could be daily or every three or four days, or so. With a drain fitting you can hook a hose to the fitting and run it into a bucket sitting next to the tank. The skimmage (waste) will drain from the collection cup when it reaches the height of the drain fitting and into the bucket allowing you to go a longer time without manually emptying the cup (like when you are on vacation).