How much water drains out of a drain hole on a yard hydrant?

The amount of water that drains out of a drain hole on a yard hydrant typically depends on the size of the hydrant and the water pressure in the system. Generally, a yard hydrant can drain several gallons of water when the valve is opened, but this can vary based on design and installation. The drain hole is meant to allow for proper drainage and prevent freezing in cold weather. For precise measurements, it's best to refer to the manufacturer's specifications.