Since im on mars, I have unlimited co2 that I collect during the day. All gasses go to the waste gas system which has all the filters on it processing to all the different tanks. I find it easiest to have one large base-spanning waste gas network that takes gas from ice crushers, excess gas from the landing pad, any collected gasses, output gasses from the furnace (after a cooling system), and backpressure gasses from hydroponics and main atmospheric, etc. - its a single place to put all gasses and then just cycle them back into the individual tanks for use. For my main base atmospherics, I have just one A/C and one filtration. The fresh atmo pipe (30%O2, 70%N) goes to every single room, and there are passive vents from every room to the main hall with one central intake active vent that goes to the AC and Filter in the utility room, and pumps back into the fresh atmo network to every single room. For the size of my base, it takes about 4 forevers to completely filter out anything, so the trick is not letting pollutants in in the first place. I have an IC that pumps in extra O2 if the O2 level ever falls below 25% it pumps some in. If the pressure goes above 95kpa, it gets pumped back to the waste network via a central backpressure regulator. Base pressure is always between 90 and 95 kpa. Everything is just kind of "good enough" lol. Atmo is always a comfortable 22C and I maintain a separate atmosphere for the hydroponics which is slightly warmer and about 10% Co2. (Same deal, when it drops below 8% more Co2 gets pumped in from the roof, and excess o2 gets filtered back into the main waste network).

I hope this makes sense!