Several ideas. Did you line the flowerpot with aluminum foil?
If you want to use your pottery kiln for burnout, it will work
OK. A little stress in opening it when hot, but this shouldn’t
be that bad. Steam dewax and you will keep your fumes to a
minimum — just use a veggie steamer in an old pot and put your
flask in so’s the wax can drip out — steam as long as you see
wax dripping out, as the moisture will actually help in burnout
— you don’t want the flask dry.
You might be able to use your hotplate and some fiberfax or
other ceramic blanket around a flowerpot or even freestanding.
Try local AP Green for the castable or the blanket fiber
Look in Tim McCreight’s Complete Metalsmith where he gives
directions for kilns for melting metal. Any of these would
probably also work for burnout.