Ummm I have just started breeding and killing my own rats for consumption of my pythons. I have found it extremely hard as my career involves saving animals not killing them........
So with that in mind, I did alot of research on what was the most humane method of dispatching rodents. And also what was the Qld guidelines for euthanasing rodents.
Ok - anything under two weeks should have its head cut off not gassed.....yes I know it does not work for those of us that use them for feeding, so second best either hit on head or whack against corner of a brick or someother hard substance, or hold rodent firmly, place rular/wood behind back of head and then yank tail down and out sharpley.
Anything over two weeks of age, CO2 is accepatable, I use the soda stream method. A soda stream machine, a short piece if O2 pipeing which I melted into the box so there was no gaps, two pumps puts them unconscious and hence unaware, two more pumps and they are dead within five mins withoout gaining conscious. To buy the whole out fit cost me $60 for machine and it included two drink bottles so I also make fizzy drink too, ($5.25 for syrup which makes 12lits, omly need tap H2o), to refill Co2 bottle if you take to BW info desk and ask for a swap it will cost you about $11 and last for about two plus months..., plastic box cost $1.40, piping left over at work, well thats the easy part - dispatching them, the costs of breeding and feeding are completely different;-)