I use horizontal nipples with a stock tank deicer. You can top off your container as needed, with gallon jugs. Below is a link for my article.
https://www.backyardchickens.com/ar...ock-tank-deicer-and-horizontal-nipples.74609/
https://www.backyardchickens.com/ar...ock-tank-deicer-and-horizontal-nipples.74609/