I own a mobile marine service in New Bern,NC. I've found on older boats thats it quite a bit cheaper to just put a new tank in rather then cut access ports and try to manually clean out the crud. Also sometimes by the time you remove the debris you'll likely develope a slight leak. For a small boat
such as yours a new tank is around $300 + 6 hrs labor and the job is done right. Also I'm not a fan of Fuel Polishing on small tanks that can be replaced as you'll never remove the crud below the pickup tube.
Power and Sailboat Repair email@example.com