Fry bacon pieces in a big pot; when nice and crispy, remove bacon and set aside.
Melt butter into bacon grease and place chopped onion in first, then add chopped carrot and celery, and finally the garlic, to bacon grease in pan and saute till softened. Add salt and pepper depending on your tastes, remember this will end up being a big pot of soup.
Add enough water to softened veggies in pan to cover slightly, let boil down a about 10 minutes. Add as much chili powder as you like (I use about a TBSP., but you can use more - it really makes the flavor of this soup) and then just add a pinch of cayenne for a little more kick.
After water is boiling and has reduced a bit, add the chopped potatoes. Add just a little more water and let the mixture boil another 5-10 minutes to help get the potatoes close to softened (they don't have to be completely cooked yet).
Once the potatoes and other veggies are close to being soft and ready to eat, add 2 cups of milk. As it is starting to heat, make sure to break down crab (pull body shell off and take center of crab and use kitchen shears to cut into 1/4, pull legs off, clean it all up, and use shears to cut just a small slit into each leg and claw piece so soup can seep into crab meat for nice flavor) and then throw Crab in with the milky veggies in the large soup pot.
Once the soup is hot and the crab is in it, make sure to turn the stove to low and try not to have the soup boil over. Add shrimp just to warm them up. Top off with the bacon pieces. Adjust salt and pepper to taste.
(If you like your soup thicker and more like chowder, you could add a mix of 1/2 cup milk and 2 tablespoons flour (shaken together in a small closed jar) to the soup a few minutes before finishing to thicken it up, if you like.). The chili and spice amounts can easily be adjusted to your tastes, it's a real flexible recipe.