> What about just one pass (because it simply *is* sufficient) with freely
> available tools?

Do you make this stuff up as you go along?!

One pass is NOT sufficient to remove the data to a point at which it cannot
be recovered. It will fool most data reading tools, but certainly not
systematic, low level magnetic analysis of the platter. For that you need to
sufficiently break up the magnetic storage to the point there it is
indistinguishable from random fluctuations.

One pass might stop your basic data scavenger - it sure as hell won't stop
the pro's.