I recently had my diesel fill hose replaced on my 87 E34. The tank was under the rear berth and then ran under the flooring to the side of the starboard lazarrette and finally up to the deck fill fitting just ahead of the transom (on the starboard side). A plywood panel had to be removed in order to get to the hose and that proved to be a real headache. Apparently, that panel was screwed into a fiberglass panel and then the waste tank was installed thereby removing access to two of the screws. So either the waste tank had to be removed or the screws sliced, and using a saw, that was the route. Once the plywood panel was removed the hose replacement was fairly easy although the new hose, CG approved, was expensive. The entire job cost $3K.
Turns out the boatyard tech noticed that the fill hose for the waste tank had a kink in it and lots of brown stain on it. The waste hose has a steel spiral wire and the brown stain was rust, so the waste fill pipe needed to be replaced as well. Of course the waste tank was half full so that had to be emptied before the tank could be replaced, so that would have meant launching the boat, traveling to a waste disposal place, before the tank could be replaced. I chose to do that job myself back at my slip since everything looked fairly accessible. Turns out that job took several days and again the new hose was quite expensive. When I did get the tank out of the boat, the fill hose crumbled in my hand so I was very close to a very unpleasant situation. Moral: after 36 years, replace ALL the hoses.