Answer:
There is a commercial product called 'Dip It' for coffeemakers. Another method involves putting undiluted vinegar in the reservoir, plugging in just long enough for appliance to heat up, unplugging, allowing it to sit overnight...then empty it and wipe/scrub.
my Rival steamer gave me grief today: I was trying to steam Tamales that were a Christmas gift. The steamer would shut off and come back on, shut off and come back on....I got mad and pitched it into the trash can, but I should go retrieve it and try the vinegar.
if one routinely pours in a small amount of vinegar immediately after cooking, it prevents that build-up...but we can't seem to do this virtuously all the time. ;-)