Why the sealing if it's not leaking? It just needs to be cleaned.
Go to Walmart and get a gallon of the cleaner that comes in the purple bottle. Mix it full strength, fill the fuel tank and let it sit or a day or two, swishing or shaking it. Dump the tank and take it to the car wash and do a couple of cycles fr pressure washing, take it home, let dry, and reinstall. I did this many times with diesel tanks in old sailboats and it gets them spotless. May as well replace the pickup tube also.
2015 Seaark 1872 MV CC
Etec 90 HP
Bitter Gun Owner