Sailing Dog is absolutely right, the seacock must be wired in the closed position.
I can't resist this obvious question. What makes you think that dumping your raw sewage in the water within site of land is a good idea? Would you mind if I came over this afternoon and took a dump on your front lawn? I apologize for the lecture but because we utilize the oceans, rivers and tributaries for recreation we have an obligation to do our part to protect the waters. We are stewards in effect.