After wasting a bunch of time setting up a filtration system with multiple branching paths that all required venting before being able to switch what gas you were trying to put into a tank I came up with this:

It's simple and expandable for however many gases you want to filter out. You'll need a filtration machine (atomospheric kit) for each gas you want to store as well as a filter of that gas type and something to store it in (portable tank with connector, tank kit, tank storage/canister filler). You'll also want to have either a passive vent into space or another storage container for the leftover waste, as well as power.

Steps to create:

• Pipe in the gas you want to filter, can be any combination/amount of gases you want
  
• Place down a filtration machine for each of the gases you want to filter out, keeping at least two spaces between them for power/piping, put a single filter inside each of them
  
• Pipe the unfiltered input into the first filtration machine and then pipe the filtered output to whatever storage method you want, connect power
  
• Repeat the last step for every additional machine but instead of using the unfiltered input use the waste side of the filtration machine (side with the power switch)
  
• Pipe the waste side of the final filtration machine to a passive vent in space or store it for later

That's it!

There are a ton of ways to improve on the system, like by adding back pressure regulators that could keep the storage from overpressurizing by venting excess into the waste pipe, but this should be enough to get started and then you can customize it to be your own. Enjoy