From my instruction book, received last week:
"Weekly disinfection:
Boil the mouthpiece assembly for 10 minutes...
OR
Immerse the mouthpiece assembly in a disinfectant of the Gluteraldehyde group..."

And under the Cautions:
"Do not put any part of the device in a microwave or conventional oven."

Nothing in the manual indicates steaming as an appropriate method. Out of an abundance of caution, with respect for my $100 mouthpiece, I am carefully following their directions.

I am glad steam cleaning is working for you. What device are you using?
Sue