Hi Bob,
Office 365 password sync via DirSync is a one way sync. That is to say, the password can only be synced from the on-premises AD to Office 365. After DirSync is deployed with password sync enabled, the synced users can’t change their passwords in Office 365. An administrator can manually reset a user’s password using the Windows Azure Active Directory PowerShell. In this case, the new password will override the user’s synchronized password and all password policies defined in the cloud will apply to the new password. If the user changes the on-premises password again, the new password will be synchronized to the cloud, and will override the manually updated password.
For more details, please refer to: Implement Password Synchronization.