Good luck with transferring her to p/k and f/t. I built my own gas chamber from stuff on amazon too. Works very well and a single tank of CO2 lasted me maybe 2 years with the small number of euthanizations I did. I would get a very small plastic bin since you will be euthanizing only one feeder at a time. Mine uses a "shoe box" sized container that will gas 4-6 at a time and for a single rat, you have to use more CO2 to fill the chamber.