You are right to be fearful.  My approach has been to fill the tank with
water while brazing or welding on it.  You need to leave a small air space
right where you are brazing or you won't be able to get the metal hot
enough.
  Rinse two or three times with alcohol afterward to get the water out.

Larry A.

On Fri, Jul 25, 2008 at 6:34 PM, Allan Streib <streib@cs.indiana.edu> wrote:

> Ed <fasteddy64@YAHOO.COM> writes:
>
> > I am doing this project next week on my 87. I decided to go with the
> > Tankit from Busdepot, it says it is all the hoses, gromets and
> > clamps to complete the job.
>
> I should probably do the same, but I'm toying with the idea to use
> copper tubing for the crossover, and braze in some threaded bungs in
> the vent openings so I can use brass flare fittings and I won't have
> to deal with those crappy plastic hose barbs that VW used.  It'll be
> way cheaper than the kit too.
>
> I'm a little fearful of trying to braze on a used fuel tank though.
>
> Allan
>
> --
> 1991 Vanagon GL
>