How do cruise ships handle sewage?

Question

What do they do with sewage, (grey water), does it go onto holding tanks to be pumped out what at a dock, or do they have their on on board sewage processing plant. How is shower water handled ?

Answer 1

Carnival's treated sewage is "cleaner than most municipal" water supplies?  Where did you get that data?   It's my impression is that most cruise sewage is mimimally treated at best.