Crockpot Manhattan-Style Clam Chowder

1 cup chopped onion

3 ribs celery, thinly sliced

2 small to medium carrots, diced

1 teaspoon dried parsley flakes

1 can (28 ounces) tomatoes

1 1/2 teaspoons salt

3 cans clams (approx. 7 ounces each) minced clams with liquid

1/4 teaspoon ground black pepper

1 1/4 teaspoons dried leaf thyme, crumbled

1 small bay leaf, optional

2 1/2 cups diced potatoes, about 3 medium peeled potatoes