I have both Eheim and Fluval cannister filters. I open them for cleaning only every six months or so. YMMV depending on your bioload. I keep BN plecos in all my tanks, probably the biggest poop generators in the FW aquarium. My filter is usually quite disgusting when I open it for cleaning.
The bottom layer of ceramic rings gets thoroughly rinsed in a bucket of tank water.
I gently rinse the upper layer of porous media in tank water. At every other cleaning, I replace about 1/3 of the porous media. I'm not even sure if this is really necessary, but I figure that the media must get clogged with fine debris over time, reducing the available surface area for bacteria to grow on. It's probably overkill on my part.
I replace the filter pad - it's too gross to even think about rinsing it, and they're cheap.
I don't bother with carbon. If your breeding fish, or keep demanding species that don't like dissolved organic compounds, carbon may be a good idea so long as it is replaced every week or two. Otherwise, it's only function is the removal of meds (which should ideally be used in a separate hospital tank anyway).