"mike regish" wrote in message
...
(they're filled in a water tank, no?),

That practice tends to be discouraged these days... It has been determined
that a slow fill is better... There are some that say that especially with
aluminum tanks, the water tank method is especially bad since the
temperature of the surface of the metal might be radically different than
the temperature of the inner metal thus increasing the chance of fractures
in the metal...