Yeah, I guess I am now an expert at thread necromancy. Didn't notice this thread wasn't touched in a year. I saw a lnk to it from another thread just a few days ago which is how I found it.
Anyway, Jairj84, I'll try to answer your questions.
I have owned 3-4 Whisper brand filters. Any recent one will have a black rough sponge in front of the filter cardtridge. This sponge is supposed to not be replaced, and it is supposed to hold bacteria. I'll assume you have one of these recent ones with the bio-sponge thing. I'll also assume you dont have the Whisper 60, which has 2 cartridges and 2 bio-sponge things.
Since you have only 1 cartridge, you have no choice but the replace the whole thing when it is time. I would just take the old one out, and put the new one in. I would not rinse out the black bio-sponge thing when changing filter cartridges. If you want, you can remove a bucket of tank water and rinse the old cartridge in it. Then you can let that old cartridge just sit in your tank somewhere for the first couple days after you install the new cartridge in your filter. This might help reduce any mini-cycle. If you do this, I would try to put the old cartridge somewhere in your tank where there is more circulation - like near the filter output or a bubble wand or whatever.
I only replace my whisper filter cartridges every 2-3 months, despite the 1 month manufacturer's recommendation. About once every 2-4 weeks, while doing a regular water change, I would clean up the filter. (I do water changes more often, just dont clean the filter every time) I would unplug it and remove the intake tube. When I have a bucket full of water from the water change, I would take the filter media (both the black bio sponge and the cartridge) and put them in the bucket. Then I go to my sink and dump the water that is inside my filter. I give it a quick wipe, rinsing with tapwater. (that is the part I had a question about earleir in this thread) Now, I put the filter back on the back of the tank. I fill up the filter with tankwater. I try to clean the bio-sponge in the bucket by squeezing it and moving it around. It usually has some debris in it. I put it back into the filter. Then, I try to get the gunk off the cartridge. It usually is really dirty. I try rubbing it, and gently scratching it with my fingers to get as much off as I can. Then I put that back into the filter. Then I put the intake tube back in the filter. Fill up the tank again. Plug in the filter.
You should never have to replace the black bio sponge on a whisper filter. They are easy to clean out in a bucket of tank water.
As you probably read before, do not rince filter material in tap water. The chlorine will kill the bacteria. Also, dont let your filter material get dry.