The one squeeze of the bulb is going to be the way i'm going to 'have' to do to start my motor. I guess every motor 'might' have that 'one special way' to start it. After all, its 38 years old and runs perfect after it has started
If your carb bowls are empty it will probably take more that just one squeeze to fill them. It is no problem you will be able to feel when the they are full. The bulb will become firm and not be completely squashed by gentle pressure.
It should not be possible to cause the carbs to flood by squeezing with gentle pressure.
It is not a bad idea to tilt the bulb up so that any air in it is swept out by the fuel, but it is not essential.
If you get all the air out the bulb will feel fairly hard when the bowls are full. If there is still air trapped inside it will always feel a bit squashy.
Just go gently and stop squeezing when you feel the resistance increase. Don't carry on like a demented gorilla.
As you now realise once the bowls are full you have to find the right technique for starting the engine without over choking.