Roughly twice a year. And by clean out, I assume you mean dismantle it and scrub it down. If by clean you mean change filter pads, etc... then I do this roughly monthly. Any more often than this you run a risk of losing a good amount of beneficial bacteria that actually keeps your water clean and clear.
Twice a year for the whole clean-up here too...then once a month i change one component of my filter...never both the carbon and sponge at the same time. Gotta keep that good bacteria happy.
