Be warned, this is a particular hobby-horse of mine.
Dame schools were an early form of a private elementary school in English-speaking countries in Victorian times and they were later considered inadequate because they often relied on the older children teaching the younger ones what they had previously learned. In this way misinformation was often compounded and no new ways of teaching could evolve using this method.
Because diving is taught in the same way as those Dame Schools, a lot of technique gets passed down from generation to generation and in that way it does not evolve. A classic example is that of the way we release air from our BCDs
during and ascent. You've probably noticed that your BCD comes with a selection of dump valves but only one inflation valve and conventionally this is positioned at the end of a long corrugated hose.
This was because when BCDs were first invented they had no direct-feed of gas from the diver's tank. They had to be fed orally, the diver taking out his regulator and blowing some air into the oral inflation valve when required. Similarly, during an ascent, excess was released through the same valve, holding it high above the rest of the BCD. To enable both of these manoeuvres, the oral inflation valve was positioned at the end of a flexible corrugated hose. Most BCDs available today still feature this hose although they don't actually need to. After all, a drysuit is used in the same way, adding air during a descent and releasing it on the way back up, but without the need for any corrugated hose attached to the suit. A hose-fed inflation valve and a dump valve are all that's required. If the corrugated hose were essential, all drysuits would have them.
Indeed, there are some BCDs available today that are equipped just like a drysuit with only an inflation valve and dump valves and no corrugated hose yet they have not proved popular in the marketplace. Why not?
Diving instructors were not born underwater. They all had to learn to dive in exactly the same way you did. The first ones to learn with a BCD were taught to blow air in via the oral inflation valve and release it in the same way. At that time it was the only option. Once they became instructors they taught their trainees in the same way.
Once direct feeds were available, they were eventually adopted but old school instructors did not want to forego the original method of use complete with the corrugated hose. Those they taught, who went on to become instructors themselves, compounded this phenomenon.
Fast forward forty years and instructors are still teaching trainees to dump air using the oral inflation valve, raising the corrugated hose to do so. Why? Because that is how they were taught themselves.
So what about those dump valves that most BCDs also come with? As usual, there will always be some misinformation offered to make the excuse for not using them. Some say that if you pull the cord on a shoulder-mounted dump valve it releases all the air from the BCD in one quick whoosh. That isn't true. Try it. They are as progressive in their action as the older method.
In fact, many of these valves are so designed that they release the air without letting much water back in the other way. That's not what you can say about using the oral inflation valve.
Some divers end up with their BCD full of water. Even if you do, by fully inflating the BCD while floating at the surface and pulling the lower dump valve, the one located near your kidneys, you can squeeze most of this water out before you need to climb a boat ladder. Remember, a litre of water weighs a kilogram once you are airside and that's more weight to carry and climb the ladder with.
Don't be afraid to use the dump valves of your BCD. They are positioned in the right place (the lower one is useful when making a quick head-down descent from the surface and you need to lose surface buoyancy) and are designed for the job. As I said earlier, there are some BCDs available that eschew the corrugated hose altogether, treating it as something of an anachronism.
So what is the oral inflation valve actually intended for? If you are floating at the surface and need to top-up the air in your BCD, you can do this by mouth just as you might top-up the life jacket that is stowed under your seat in the aircraft you went on holiday in. Of course, there are some kit manufacturers who pander to the resistance of some divers to take on board modern developments in kit and these provide BCDs with only a corrugated hose and no dump valves. They still work just as you could even use an inverted plastic carrier bag for buoyancy control. It's just not as convenient!