Bob, just noticed you said thru-hull fitting. On my 89 204c, the thru-hulls are adjacent to the cockpit drains in front of the helm and passenger seats. I have a 6" access plate on each side that were on the boat when I bought her. I don't know if they came from the factory or a prior owner put them in. I can at least touch the thru-hull fittings, get to the clamps, etc. but it would still be a bear to do.
The hoses from my fish box drains run forward to a "T" that connects to the cockpit drain and the thru-hull. I thought long and hard about replacing everything while I was at it but decided I had enough irons in the fire for now. Maybe this winter.
I spoke with some of the local boat repair shops around here and was told they now just cut holes in the deck to get access then replace the section and reglass. In some boats, there are apparently no alternatives.
Gary 89 Overnighter