The gunk can be scrubbed out of the throat using a "soft scrub" pad made for acrylic tanx. Those little white Spirorbid tubes can simply be scraped off with a plastic scraper. The rest can be soaked in a solution of white vinegar and water (1 cup per 5 gals is fine). I'd disassemble the pump from the unit and let it run in the vinegar bucket for awhile too.
