Just curious here for the "for dummies" explanation - I've used a skimmer for years in my sump - I have dismantled it for cleaning many times - it works well I know that because of the sludge I clean out of the top weekly...but damn the thing is just spinning up air bubbles - why/how does this attract the sh!t it does? Do the walls of the chamber need to be clean to somehow force the stuff to stick?