ANFPO- please elaborate. i dont understand your suggestion. I have always known the washer be on the other side of the nut.
The important part is to have a nice flat sandwich of rubber between the shoulder of the bulkhead and the wall of the tank, whether the wall is on the outside or inside relatively to the shoulder.
Its perfectly fine for the gasket to end up on the dry side. Actually preferred, that's why they get stiffed when installed saltwater side.