Them
Contributor
Pretty much identical to using a snorkel keeper. Curious about the square shape, though....
The idea is that the square is passed through the circle (to attach the keeper to your d ring) and the octo mouthpiece is passed through the square.
That's what I used during OW training...actually I asked how the octo should be held and the instructor disappeared into the shop and returned with one. It worked but I did manage to have the octo come out of the keeper twice and I never figured out how to mount the octo quickly.