Shrimp and Crab Boil

extra large onion , peeled and quartered

large garlic cloves , peeled and smashed

vegetable or canola oil

ketchup

Couple dashes of hot sauce

freshly cracked black pepper

Cajun seasoning (like Slap Ya Mama ), or to taste

large lemons , sliced

white vinegar

liquid crab boil , or to taste

of a 1 pound bag of loose crab boil seasoning (like Slap Ya Mama ), divided, optional

andouille or other spicy smoked sausage , cut into 3-inch sections

About 10 new potatoes or very small red potatoes

ears of corn , shucked and cleaned, cut into thirds

to 5 pounds of large (16 - 20 count) raw shrimp , shells and heads intact

kosher salt