Here ya go:
If you want an inexpensive, easy way to keep your tank from freezing, you can wrap it. Buy 2" upholstery foam (you an get it on eBay). Slide it into a heavy duty contractor bag. Secure the bag tightly around the foam. Wrap the bagged foam around your tank and secure it with duct tape. Voila, insulated tank. For an extra layer, you can float a piece of insulation board smaller than the surface of the tank. it will keep the water somewhat warmer, and as it moves around on the surface will help to prevent freezing.
I didn’t see the manual fill option when I looked at them. I still think having animals on a property with no water supply is risky during the Winter when you have ice as a possibility.