1. Make sure that the dive shop gives you all the port plugs they remove from the first stage when they attach the hoses. These are expensive to buy separately and there is a good chance you will need them.

2. Choose a second stage with an exhaust tee that extends far enough out to each side so the bubbles you exhale will travel along the side of your head, rather than up in front of your mask.

3. Having chosen your ideal second stage, buy two of them. Do not make the common mistake of buying one good second stage and one of the cheap “octopus-only” units that some dive shops supply in package deals. These are cheap for a reason. They will probably breathe wet and be more inclined to free-flow. Also, bear in mind that somebody, either you or your buddy, is going to have to breathe from your octopus at depth one day, possibly in an emergency. That is why you have your octopus after all. It is not just for show.

4. Decide which second stage you will hand off to a diver who comes to you to share air: the second stage in your mouth or your octopus. Make sure this second stage is attached to a hose that is long enough to allow the other diver to swim a little away from you, so you don’t get in each other’s way as you ascend.

5. Decide where you will keep the second stage that is not in your mouth. Wherever you keep it, it needs to be secured so that, a) it will not come loose b) it can be reached quickly and easily, and c) you can deploy it with one hand.

6. If you decide on an inflator regulator as your octopus, make sure you attach your main regulator to a long hose because that is the one you will be giving to a diver who comes to you to share air. You will not be giving them the inflator regulator.

7. After you hand over your main regulator, you will be breathing from your inflator regulator and controlling your buoyancy using the BCD inflator mechanism, which is now in front of your nose. This is a skill that needs to be practiced a lot. It is not something you want to do for the first time in a genuine emergency when you are attached to a stressed diver who a few minutes previously thought they were going to die!

This blog post is adapted from a chapter in Scuba Confidential: An Insider's Guide to Becoming a Better Diver​.