Hi love_fish
If I remember my old Whisper filters, they have a cartridge that has a fibrous bag with carbon inside it, right?
If you open the top, you should be able to remove the bag and dump the carbon out. It has a plastic frame holding the bag in shape. If you do this under water taken from the tank and rub the bag gently with your hands to remove the gooky stuff from it, it will clean up nicely. You can forget about the carbon since it's probably old and not really needed anyway.
While you are still working underwater, put the bag back on the frame and put the top clamp back on. It's then ready to put back in the filter and will probably still give you lots of service. Since the bacteria live on the strands of the bag, you are not losing them when you wash away the dirt.
The only time you actually have to replace them is when they start to tear up. Then, you can open a new one and dump the carbon out. You can stuff the old bag (after it's been cleaned like I just explained above) into the frame and replace the top. Get it right in the filter and you will have lost very little bacteria.