Items you’ll need for storing and cleaning your catch include a bucket, a sharp paring knife, kettle, and gloves.
Like other shellfish, geoducks must be kept alive until they are cleaned, and should be cleaned as soon as possible after digging. Place them in a bucket and cover with a cool, damp cloth. Don’t immerse in water or airtight container. Keep them in a cool place, out of direct sun.
Rinse all sand from the geoduck, blanch them in boiling water for 10 seconds and then submerge in cold water.
Scrape a knife along the inside of the shell to cut the adductor muscles. Use gloves to avoid cutting your hand on the sharp shell edges.
Pull out and discard the visceral mass, consisting of gills and stomach, leaving the siphon and mantle.
To peel the tough skin off the siphon and body, place the geoduck in hot water for about 45 seconds. Peel the skin starting with the body and continuing off the end of the siphon.
Wash the clam thoroughly.
Split the siphon by inserting a knife or scissors and cut the siphon lengthwise. Wash the siphon, removing all traces of sand and grit.
Siphon meat is firm and tough and can be sliced thin at an angle and pounded gently with the smooth side of a meat mallet to tenderize into thin steaks for sautéing.
The meat of the body is more tender than the siphon. Split the meat down the median line and chop. Tenderizing is not necessary if you intend to use the siphon or body meat in chowder.
Here's an interesting video on how to clean and prepare Geoducks.