In June I purchased a 1999 Hunter 420 CC that was basically used as a floating condo ( only 60 hours on the engine). The main problem is they didn't really maintain the boat particularly the holding tanks. The odor was horrible below deck. After multiple pump out and flushing it marginally improved. My wife is blessed with a very sensitive smell and therefore it quickly determined we had a very big problem. I laborously changed out the hoses that were accessible. The hose from the aft cabin head to the vacu-flush system in the transom area is hidden behind fiberglass covering for about 12 feet and is not accessible ( based upon the difficulty removing the "accessible hose" that is mainly accessible). I would have to cut away the fiberglass to replace that long length and then reglass it in. There is a small length or 1 1/2 inch line that I couldn't get in the forward holding tank that goes forward behind the tank and fiberglass panelling that also seems inaccessible. Otherwise, I have replaced all the hoses except the small vent lines. Still the odor is very strong. I am about to move on replacing the tanks as that is the local's advice that the liquids have been permeated into the tank material. Forum comments seem to question this logic. What is the best approach next ????