in my sump its setup like this

Water enters

chamber #1 where it goes through a protein skimmer and carbon reactor
Chamber#2 it flows through Filter mesh and sponges
Chamber #3 Rubble Rock and Macro then it returns to the main display.

The skimmer pump and reactor catch some detritus, the filter mesh and sponges catch almost all of whats left to catch. By the time it gets to the rubble im not worried about it. Probably every 3 to 4 months I will stir up the sump good during a water change and completely drain it. Im not a heavy feeder so this also helps keep my system clean.