I read Eric's document a few years ago. Make sure you read it carefully.
Learn the Frenzel, then the mouthfill. Then you can equalize everywhere
I usually fill my mouth at around 35m (maybe no need to do it so deep). Has taken me to 72m with ears and mask equalized at the bottom. I like to equalize before I turn around. I had air to spare, so I could equalize ears and mask even deeper.
If you don't equalize your mask very deep, then you can save a lot of air. I once did a variable balast dive (holding on to the bottom weight) using no mask, just a nose clip. The bottom was at 53m but still I was surprised to see how much air I had in my mouth. It was almost full.
To fill my mouth I use my throat to "pump" air in my mouth. To those who ask, I describe the whole thing like this. "Try to laugh the way Santa does, only with your mouth closed".
