Making the Connection
The fishbox is just aft of a bulkhead. We cut a 3-inch-diameter hole in the bulkhead and then a 2-inch hole through the fishbox. Reaching through a hatch, one person can slip our modified through-hull fitting through the bulkhead and into the box, and then install the nut on the inside of the box.
To ensure that the holes in the fishbox and bulkhead lined up, we drilled a ¼-inch pilot hole through both using a speed square to ensure the bit was level and straight. Hole saws finished the job.