Have metal tanks back from the 50's with no rust. My trick was to keep a little 2 stroke oil mixed with gas in each tank and slosh it around every so often. When the fuel begins to stink change it out for fresh. My old tanks are more collectors and conversation pieces but with new gaskets could be made to use. Just gotta remember to slosh the fuel around...when someone inquires about them is my reminder to slosh
If the gas stinks it's gotta be preeettttttyyyy old.
The OEM tank that came with my 9.5 Rude is now 52 years old. I do remember replacing the fuel line once, but it has lasted all these years without issue. Of course, it's a 2-stroke so oil is always in there regardless.
A few years ago the gauge stopped working. The cork float sank because the E10 dissolved the lacquer it was coated with. Thus, I had to pull the top cover. The recommendation was to replace the cork with a neoprene stopper and that did the trick.
I thought I would clean it at the same time, but other than a few small sand-like pebbles, the inside of the tank was clean and shiny.
One of the largest internet suppliers of obsolete boat parts is right down the street from me, so a new gasket was had for only a couplabucks.
For rusty tank bottoms, after draining the gas I put in a couple gallons of soapy water along with a couple handfuls of nuts and bolts. Then, shake and roll. After draining again stick in a hose nozzle and the high pressure will loosen any remaining corrosion. Finish with a bottle of isopropel alcohol to disperse and remove the water. A hair dryer removes all traces of alcohol.
