Well that was fun, the perfect remedy for COVID boredom. After a clean out using brand name “gas tank cleaner” from O-O-O ORLY’s that was useless, I did a white distilled vinegar soak for 5 days and then a pressure washer at 1500 PSI with water which worked great. 16 years worth of old gas sludge and small embedded pieces of the old sending unit float gone. A heat gun then alcohol to get water out and a bit of new gas sloshed around and inside of tank was ready to go.