Natarajan Krishnaswami wrote:

I combine flushing and pre-heating, I put only a little water
to do both, maybe about 2 oz? Then I swish that water
around. I think it preheats the thicker base of pot enough
and heats up the sides a bit. I would do this even if
pre-heating did not make any difference, just to
flush out dust get leaves to open up more if the tea
is whole-leaf. I don't preheat the second, thin-walled
glass pot where I pour tea after infusion. I would say
that with thin glass pots this is completely unnecessary,
with thicker glass pots I'd have to experiment but my
guess would be it also makes little to no difference.