look in your local YELLOW PAGE directory
for "Automotive Radiator Repair" shop.
Let professionals 'boil' it out for you & leak test the seams.
They will return it clean, soldered, and painted for surprisingly
little money.

Or just replace it with a new tank and have insurance against future
fuel system failure for the nest 28 years. New is available from any dealer.
_________________
1976 BMW 2002 #2743711(sorry I sold it 12/25/06)
1986 BMW R65 650cc twin 19k miles
1964 BMW R27 250cc single 15K miles
2002 BMW 325xiTouring 29k miles
1984 MERCEDES-BENZ W123 300D Turbodiesel-188k miles fein-DIESEL