I am using that double one that you have pictured.. The first stage (right side pictured) is more of a gravity filter which works well. The second stage came with a nice heavy walled clear tube with O rings on each end. It was filled with carbon. The ends are threaded but they are glued in place. The filter is meant to be replaced after six months. There is a small hole on each end (maybe 1/4") with a thin mesh/felt type filter inside. I pulled out the top filter, poured out the carbon, and replaced it with X13 Zeolite. It worked out pretty neat.
After using it the first time I released the two drain lines and a good bit of moisture came out of the first stage.