don't clean them,I know some people that did not clean their filters for over a year,if you clean the filter all the good bacteria's will die!!
filters which haven't got cleaned for longer period of time have way more bacteria's and that helps to keep water excellent,I did not clean my filters for over 2 months and they work way better then before,I use to clean them each week during an W/C but some one told me that is better too not clean them so often but it all depends how big is your aquarium and how many fish's you have there but also filter volume and flow is important.
I got two fluvals 405 on my 160 uk gallon aquarium with two Oscars and water is perfect for over 14 days but i do 50% W/C every week anyway.