RE: trawler needing to be towed from Boca Del Toro, Panama to Colon, Panama & DD 453's replaced
I would plan on using FRESH fuel with a simple setup to run from 55G tanks on deck.Hose is cheap.
After you get to your repair spot you cam drain the old fuel, to get into the tanks.
The tanks will need to be opened and scraped clean with a tool (wood spatula?).
After the tanks are cleaned - or simply replaced , you can decide if 3 passes thru a Raycore will be enough to clean the fuel.
STARTRON is for mild problems , not what you are facing,and may create problems of its own!