Jeff Marchand wrote: A heated stock tank that I can drain to the outside?
Temperature is one of those relative things. Getting out of a hot shower into a 15C room would seem to me, much colder than getting out of a cold shower into that same room. For that reason, my gut feeling about a heated stock tank is that I wouldn't do it.
We don't get much super cold weather, but if they're calling for freezing, or we get snow, I use rubber buckets with relatively small surface area for the ducks. They will still try to have a "sponge bath duck equivalent" and make plenty of mess, but they've been OK.
However, yes, they need to clean their nares and eyes daily. The easy way to encourage that is we soak whole wheat overnight, drain it, and pour it into the bottom of the bucket. The ducks all love to dive for it! It also gives them the extra B vitamins that ducks need, so it's a double win.