btw, some skimmers, like my IO seaclone, are impossible to take apart and clean.
solution.
leave them to seep in vinegar water for a few days, then pick it up and shake it while their is water inside. this nocks all the gunk off.
and go figure, i see decresed efficiency when i clean the collection cup. I think it has to do with the bubbles having to pass over the semi moist glass, or the very moist gunk. Bubbles will break if they touch a dry surface, you can test this out yourself. try and put your dry finger through a bubble. it pops. now try it with a wet finger. Its magic!