Del Johnson wrote:

I like this idea, which has surfaced before, but where does one
purchase a floating magnet that could move up and down a small tube
and be immune to fuel degradation?

I can't speak to the "floating" part, but labs use magnetic stirrers
which are bar magnets encased in completely non-reactive plastics of
some sort.  I used zillions of them years ago.  You can probably get
them from Edmund Scientific.  Yep: p/n 3108000 seen at:
http://www.scientificsonline.com/Product.asp?pn=3036284&bhcd2=1125434694

Everything you ever wanted to know about tank level sensors:
http://www.sensorsmag.com/articles/1204/15/main.shtml


Russell Kent