A well running sump requires much less cleaning than a cannister filter. Once your bacteria colonies are established, you will not need to really "clean" the sump (as in stop the sump, remove the filter media and rinse it in fish tank water and/or replace some of the media) more than once a year or even two years; the variables are the size of sump, size of tank, kin of filter media used, stocking level of tank, and amount of food entering the tank.
You may want to either clean or rinse out the very top filter layer of the sump once every week or two in order to help "polish" the water; it is the top layer of filter floss and Japanese mat that is the initial filter and that catches most of the larger particles of fish waste.