I assume southstar066 is referring to rinsing, shaking, whatever process you have to remove waste.
Dependent on growth, I get rid of about 2/3 every month or so. At minimum I give it a good dip/rinse in a bucket of tank water at this time. It really depends on how much junk you have getting in there. I would say try it every couple of weeks, and if you can't see the bottom of the bucket you're rinsing in it might be worth doing it more often.