Melt the clarified butter in a large saucepan over medium heat until a pinch of flour sprinkled into the oil will just begin to bubble. Whisk in the flour to form a thick paste the consistency of cake icing. Continue cooking, whisking constantly, until the flour turns the colour of melted chocolate, about 45 minutes. Slowly whisk in the water and bring to a simmer. Whisk until no lumps of roux remain; set aside.
Meanwhile heat the olive oil in a large pot over medium-low heat. Stir in the onion, okra and green capsicum. Cook and stir until the vegetables have softened and begun to brown, about 30 minutes.
Stir the tomato paste into the okra mixture until no lumps of tomato paste remain. Add the tomatoes, garlic, salt, black pepper, bay leaves, seafood seasoning and roux-thickened water. Bring to a simmer over medium-high heat then reduce heat to medium-low, cover and simmer 1 hour.
Stir the prawns, crab and oysters into the gumbo, recover and cook 20 minutes longer.