A reader points me to this interesting post with lots of details and images showing how the Apollo 13 crew and support team on the ground devised an improvised CO2 scrubber from miscellaneous items available in the Command and Lunar Modules : This is the actual hack that saved the astronauts of the Apollo XIII – Sploid
After Mission Control decided to cancel Apollo XIII’s moon landing following an explosion of an oxygen tank in the Service Module, the astronauts moved to the Lunar Module in order to save power that was going to be needed later for re-entry.
The only problem with this plan was that the Lunar Module was designed for only two people for a 36-hour period, not three astronauts for 96 hours. They quickly discovered that carbon dioxide was building up fast, putting their lives in extreme danger. They had to change the circular CO2 scrubbers in the Lunar Module for clean ones, but they only had spare square CO2 scrubbers from the Command Module.
In record time, the Crew Systems Division put together an improvised adapter using all sort of weird and random parts, like a flight manual cover, suit parts, and socks. CAPCOM (Capsule Communicator) transmitted the instructions to the astronauts in order to assemble this “mailbox” rig—as they called it—working against the clock and trying to surive fight the effects of the poisonous gas which was quickly asphyxiating their brains.