Cleaning a ballgown can be an intimidating process and many people have different opinions and experiences on how it can or should be done. You can research on forums for tips and tricks, or even ask the dressmakers themselves (who usually have some great advice)… but one thing that everyone can agree on is this: do not bring your costume to the dry cleaner.
Here is an interesting video about dry cleaning will help understand why it’s not a great idea.
(also, read THIS ARTICLE over at Dance Comp Review for tips on cleaning costumes)