Rinse winter melon under running water; Scrape out the seeds; Peel it with a Y-shaped peeler; Cut it into chunks.
Rinse, drain and cut Chinese pickled radish in sections.
Grab crab with your left hand, with your thumb pressing the cardiac stomach and the remaining fingers pressing the left claw; Loosen the strings, grab and pull the right claw up with your right hand to separate the right claw from the crab (repeat the step for the left claw); Break off and discard the mandibles (i.e. mouthparts) with a pair of scissors; Remove the abdomen (i.e. apron) with your fingers;
Remove the outer shell (i.e. carapace) by sticking your thumb into the hole left from removing the abdomen and lifting up firmly; Brush clean the crab legs and the carapace; Remove and discard the leaf-like spongy gills from either side of the body; Rinse out the greenish-brown guts, and translucent heart; Crack the claws with the back of the blade of a knife.
Fill a stockpot with 2.5L water; Bring to the boil over a high heat; Add the winter melon, the Chinese pickled radish and the ginger, and bring to the boil over a high heat again; Turn to a medium heat; Cover the pot with its lid; Cook over a medium heat for 30 minutes; Add the crab; Cook over a medium heat for 10 minutes; Stir seasonings into the soup; Turn off the heat; Arrange the soup into serving bowls.