Rodent euthanizer

Looking for a kill box setup to humanly euthanize surplus rats. Not afraid of DYI but would prefer a well built set up. Don't really need volume so smaller unit will do just fine.

Was able to make one out of a few common materials. Took a rubber made container and secured a valve to it. Purchased a co2 tire inflator (genuine inovations ultraflate avaliable at REI and Walmart for 15) and it works great. I picked this unit because it uses the non threaded co2 cart rages avaliable at Walmart (40 for $17).

If anyone was looking for an inexpensive humane way to do FT this is your answer. I use 1 co2 per 6 rats. Could likely do more but this seems to work well. Entire process takes a few minutes.