Draw a vacuum on your housing to check for leaks prior to entering the water. It's a simple check that helps you guard against large, catastrophic leaks.
Use the hand pump to create a vacuum inside of the housing. Wait for a few minutes or several hours and check to see that the vacuum has held.
Watch the video to learn how to install a vacuum valve on an existing housing, and how to get your housing ready before a dive.
Skip to 4:50 if your housing came with the vacuum valve installed.