Re-using the solo Spacefarer modules - what am I missing?

So, got my first mission completed. Now I want to go up again. So I want to purge the atmosphere from the solo spacefarer module to and reset it. How? I've tried hooking up the input gas pipe to my O2 supply and that worked - but the CO2 is still inside the module, despite me connecting the output to a vent.

Do I really have to build a gas pump and a generator inside the module just to push the CO2 out to prepare it for a new mission? Or am I doing this wrong. The whole rocket UI seems very counter intuitive to me at this point. Thanks!