There are two types of models for Outdoor Fountains and Bottle Fillers in areas where the temperatures drop below freezing, freeze resistant and sealed (or sanitary) freeze resistant. While the models use different valves, both of these models are installed below the frost line and extends the length of time throughout the year that these can be used while alleviating the need to winterize.
For a freeze resistant model, the fountain or bottle filler is designed to have it's valve installed in the ground below the frost line. This is usually anywhere from 5" (127mm) to 72" (1829mm) below ground level. When the unit is activated, the vent line pushes into the valve which then opens and forces the water held below the frost up through the unit to be dispensed.
Sealed (or sanitary) freeze resistant models have all the same features of the freeze resistant model with the added benefit of the valve being inside of a sealed canister. This sealed canister minimizes ground water contamination and prevents drain water from mixing with fresh water when the model is being installed in areas where the water table can rise due to inadequate drainage or in areas where flooding can occur.
Example of the Sealed Freeze Resistant installation.