Sorry it took so long to get this information out.

Hot Rod Bikes magazine July '97 issue contained an article about a
company that treats rusty gas tanks.  I have never used this companies
products or services but the magazine usually has good information.
Anyway a synopsis follows:

The company's name is Rusteco.  They will either treat your tank for you
or sell you some of the solution they use. The solution is called
Rusteco R-200-3 and they claim it to be fully biodegradable, nontoxic,
nonhazardous and noncorrosive (except to rust, I guess).  They show a
photo of an ungloved worker removing a painted tank from a vat of the
solution with no apparent damage to worker or paint job.  They say used
solution can be reused as garden fertilizer. "?"

They dunk the tank for 4 - 24 hours and the article claimed amazingly
good results.

There are two sites available:

Rusteco Service Center, West
Dept. HRB07
2029 W. 16th Street
Long Beach, CA 90813
800-787-8326

EcoClean, East
Dept. HRB07
100 North Meadows Road
Medfield, MA 02052
888-399-2600

I can email out an image (B&W) of the article if anyone is interested.

Bill Kenneke  kenneke@clis.com
'85 Wolfsburg GL, "The Cool Camper"