Final answer:
The two most common methods for recovering a regulator that has fallen behind the shoulder are Reach, Blast and Sweep, Purge. In the reach and blast method, you forcefully exhale to clear water, while in the sweep and purge method, you remove the regulator and blow into it to purge water.
Step-by-step explanation:
The two most common methods for recovering a regulator that has fallen behind your shoulder are Reach, Blast and Sweep, Purge.
In the reach and blast method, you reach behind your shoulder and grab the hose of the regulator, then forcefully exhale to clear any water that may have entered the system.
In the sweep and purge method, you use your right hand to sweep from the velocity toward the magnetic field with your fingers through the smallest angle possible to remove the regulator, then blow into it to purge any water.