I bought these and just slipped them over. I tell you what.. they work wonders with keeping the big stuff out! when I clean them.. I just take a ziplock bag and put it over the sponge and slip it off into the bag as to not get all of the debris in the tank.. rinse it out and put it back on! works great!
here is what I bought
http://www.petsmart.com/product/inde...ductId=2752618
they just slip on over the intake strainer!