Esri used to have a forum sticky that contained the login instructions to the FTP site for the Arc Hydro tools. They have since deleted all of their forums.
Does anyone know the login instructions for the Esri Arc Hydro FTP site?
The content was migrated to GeoNet over the fourth of July weekend. A quick Google search turned up a relevant thread (read the top and bottom, because the password has changed since the original post), so GeoNet has been at least partially indexed by Google.
Note: I turned up a possible link to the old forums on a private GeoNet group, but it's not working. If it gets fixed, or another link is posted, I shall endeavor to add it here.
mkennedy's link explains it but here are the details in case those posts go missing again:
Set your SFTP client to log in to:
It appears that they just change the year in the password, so if "ADSRiver.2014" doesn't work, try the current year.