I think I can kinda relate....as far as looking for a way to keep the biomedia gunk free......
I have my drip tray full of about 2.5" of polyfiber and my pot scrubbies still get impregnated with gunk over time.....although,as Joe mentioned it still takes about 6 months before it gets bad enough that I need to clean out the sump.
However,contrary to what some have said I do need to use something with a bit of pressure to get the crap out of the pot scrubbies...and the nylon ones are harder to clean than the plastic ones.
what I do is just take the whole thing outside and plug in the pump and let it shoot up like a fountain,cleaning my scrubbies in its flow....but then my tank goes through a mini cycle for about a week and a half, two weeks.
I never saw a question posed, only someone sharing how they handled gunk buildup in their sump.I,in turn, shared how I usually take care of the problem.