My routine is similar, except that my step 3 is a further “sipping” inhale, repeating your step 2 and my step 3 until I can’t take in any more air or hold my breath any longer. I’ve found that the initial “max capacity inhale” really isn’t that, but it takes some seconds holding that much air in at rest, with the trachea closed, in order to further inhale.

I think my version works because the diaphragm can’t spasm when it’s stretched (or contracted, not sure which) so far out from its neutral position. If I think of it next time, I’ll have to try your method out!

I do something similar that also works 100% of the time!

1. Inhale until lungs are at full capacity.

2. Hold your breath as long as you manage comfortably.

3. Breathe in and out slowly for a couple of breaths. I.e. don't gasp for air.

I also long suspected it may work by reducing the activity/stimulation of the diaphragm.

This might just end up doing the same thing with extra steps but for me the most effective has been holding breath until it starts to become slightly uncomfortable and then start drinking a full glass of water while allowing myself to take short breaths of air as necessary between swallows. Something about the swallowing motion combined with short breaths seems to "reset" the diaphragm like a champ for me. Breathe slow and relaxed for the minute after to ensure it's really gone :)

Anecdotally, a friend's mother can stop pretty much all hiccups by putting pressure somewhere on the wrist. I'm not sure about how it works, but it does.

Her own wrist, or someone else’s?