Fill the large pot 2/3rd of the way with water. Add 1/2 cup of salt for every gallon of water. Bring the water to a boil.
Add the crab(s) to the pot of water; ensure they are fully submerged. Wait until the water returns to a boil and then start a timer for 20 minutes. When the timer ends, the crabs should have turned red.
Take them out of the water and place them on the kitchen towel.
Fill a large bowl with cold water, and place the crabs in the cool water for 5-10 minutes. This will help stop the crab meat from sticking to the shell.
Once the crabs have cooled, remove them from the water.
Move a crab to the sink. Under cold running water, flip the crab over. On its belly, you'll see its apron—it's circular on a female crab and pointed on a male crab. In the picture below, the apron is pointed, so we know it's a male.Use your thumb to flip the apron away from the crab and then break it off, away from the shell.
Stick your thumb into the hole left after removing the apron, and use it for leverage to remove the top shell and carapace from the crab's body and discard it. At this point, crab "butter" and guts may begin to fall from the crab. This is normal. Rinse the crab's body under running water to clean it off.
Remove the crab's gills, otherwise known as the "dead man's fingers". They're rubbery and spongy. Pull them off the crab and discard.
At the front, near the crab's mouth are its mandibles. Crack them off and discard. Rinse the inside of the crab's body thoroughly again under cold tap water. There shouldn't be any more guts, only shell and legs/claws.
Flip the crab around, hold the center of it with both hands and crack it cleanly down the middle like you were opening a book.
Rinse the legs and claws thoroughly under cold running water once more. Pat the legs and claws dry with a paper towel.
Use a pair of kitchen shears to snip off the tips of the crab legs so they don't poke through the freezer bag.
Put the crab legs into the freezer bag, gently squeeze the bag to remove as much air as possible, and seal it.
Straw "vacuum seal" trick (optional): Slide a straw into the bag and suck out the air so the bag "shrinks" around the crab legs. Slide the bag down the straw as you inhale, and quickly seal the bag while you remove the straw.
Write today's date on a freezer label, and stick it to the bag. Place the freezer bags deep in your freezer.