Wasn't that bad in my A plan, Just remove the back of the hanging locker to access the vented loop and cut the hose into short pieces with a jig saw. When I installed the new hose I put a ball valve in line
to allow for easy head repairs
For the tank to deck fitting I had to crawl behind the engine to pull it through and guide it up. I got lucky at the deck fitting as mine is on the coaming and by removing one of the storage bins I could reach in and access the tail of the deck fitting.
Use the best hose you can get for the tank to head section to avoid odour and doing the job again.