I can't count the number of suction cups I have, including big ones (eheim heaters) that don't stick anymore. I've tried to remove them and wash them in warm water, scrub them as well as the portion of glass that they go on, but nothing seems to really work well. Any special tricks out there?
I know of the ones with magnets on the outside, by the way, like this one here: https://www.jlaquatics.com/zoomed-ma...ction-cup.html. Those work great but they are kind of pricey.