In most areas with a large yachting presence and commercial fishing fleets, one can usually find commercial tank cleaning/fuel polishing contractors who also have the capability or the resources elsewhere to put access ports in the fuel tanks. You could start out by seeking the tank cleaning/fuel polishing service providers and asking them where you can find an experienced tradesman who can add access ports. You will need at least two and you can be guided by the marks made on the tank exterior where the internal baffles were welded. I am not near the sea today so perhaps someone could take a photo and post it here of a late model Super Maramu tank top with the access ports as done by Amel. Early series SM 53 also did not have access ports in the fuel tanks until about 1997, but I am not sure of the actual date these ports were incorporated.
Make sure the ports are big enough to allow access to the entire interior of the tanks in order to perform a complete cleaning of all internal surfaces. Otherwise, any biologic material will just regenerate and start the ugly cycle all over again.
Hope this helps you, Joel
JOEL F. POTTER-CRUISING YACHT SPECIALIST~L.L.C.
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