How clean do you keep your sump?

[KPG007]

In over 3 1/2 years I had never cleaned out my sump before. I recently shutdown my 60g, and had to clean everything out. I was surprised to find that the sump contained about 2 inches of muck! The tank ran like a dream though and the water was perfect.
In the future, I will probably keep a closer eye on it, but if there are no issues, I don't see a reason to clean it.

PS - Lots of bristle worms ect, living in that muck, so one more reason to leave it be.