The idea of a cookie tin heater is great but what scares me is the hazard 110 volts under a bucket of water presents. A lot of folks run an extension cord never thinking to use a GFI outlet.
Just my thought on water heaters. Rather than mickey mouse something like cookie tin or fish tank heaters. Both I thought might have a limited life at best or a danger at its worst. I bought a bird bath heater they are made for the job operate on a thermostat safe and economical to run. I also...
I have horizontal nipples in PVC pipe. I use a tabletop fountain pump to circulate the water from the end of the run back to the pail. Cheap $12.00 AND SAFE!!! Running water does not freeze.