What is necessary to ensure a dry-barrel hydrant drains completely?

To ensure a dry-barrel hydrant drains completely, it is essential to leave the discharge cap off until the hydrant is fully drained. This process allows air to enter the barrel as water is expelled, facilitating the complete drainage of water from the hydrant. Without this action, vacuum pressure can form, trapping water inside the barrel, which can lead to freezing and potential damage during cold weather.

The other options do not effectively contribute to the complete drainage of a dry-barrel hydrant. For example, leaving the main valve cracked open could prevent a full drainage cycle and allow water to remain trapped inside. Similarly, replacing and tightening all discharge caps air-tight could inhibit airflow necessary for the drainage process, while re-tightening the air-bleeder nut does not significantly aid in the complete draining of the hydrant. It is crucial to ensure that the discharge cap is removed to allow for effective drainage.