Charles Spitzer wrote:
....
i have a similar problem of rusty hot water, but only at a single point
(tub). the 2 adjacent sinks don't have this problem. this has puzzled the
plumber who installed it, along with the contractor. any ideas?


Galvanized line to the tub hasn't been replaced, other has...

new construction. all copper piping. only 3 years old. i doubt very much
there was galvanized line, and the installer stated they didn't use any.

You didn't say that initially...

Something in the tub fitting set then or some trash left in the line
would be next most likely...