I really don't want to further hijack the thread.
Why bother with two waterers needing to be heated?
Plus they won't use the HN's of other water is always available.
Have seen ducks use the Horizontal Nipple's...and they have spring loaded valves...so your shower is unlikely, but I guess a constant dribble to puddle is possible.
Nor sure I'd trust a cheap heater or that it would keep the trough thawed....and you'd have to make sure the cord hole was sealed...
You could train them to drink from Horizontal Nipples,
but it wouldn't take care of rinsing nares.
Not sure an aquarium heater would be suitable in an open waterer.