How do you remove the nasty gooey residue from tank?

[3dachshunds]

I am working on new to me 1992 K100RS. The bike set for at least a decade with old gas in tank. I emptied the tank and hoping to remove as much crud as I can. Has anyone cleaned the tank from
rubbery residue? Should I wait until inside is bone dry and scrub with plastic spatula, or should I try to dissolve it? It seems acetone dissolves this stuff well.

[Atabeach]

I recently acquired a 1985 barn find ( see post ) that had been sitting for…a decade or two. Removed innards and used White vinegar overnight….the next day.... hand in tank... scrub with a scotch brite! Two applications. PS try not to get vinegar on paint.

[Kaos]

Atabeach is correct, vinegar, cleaner, calcium remover and fresh gasoline could work as well.
Dont mix them, and after soaking and brushing, rinse thoroughly with water.
Do keep in mind that the tank is aluminium and a high acidity (if i recall correctly above 10%, do check this on beforehand) will bite into the aluminium.
Also i used a dishwash brush with a round head, works like a charm. Not when using gasoline tho.