Well, i just got through cleaning mine after not doing so for about 2 years.Let me tell you, it smelled so much like dirt it wasn't even funny.There was literally 1" of goop in the bottom of each canister.The filter floss was so disgusting that i didn't even want to touch it.The sponges in the bottom were so covered in gunk that i don't even know how the filter pushed any water.
Lol, i did find a couple baby crayfish in the bottom, i don't know how they managed to live down there.God only knows what they ate....Shudders
My only suggestions, throw them out and buy new filters!
What you will see cannot be unseen!
All kidding aside, good luck