We were on the Caribbean Princess last week. It is a ship we have been on many times in the past, and unlike a few posters who experienced their version of a "cruise from hell", we really had an overall very good trip. One of the issues we had was a non or slow flushing toilet. Although we have experienced toilet issues on multiple cruises, it was a little different this time. I am hoping @chengkp75 sees this post and can offer some insights on what the underlying problems may be.
OP, without knowing how much you know, or want to know, about toilet systems, let me get into a discussion based on some of your symptoms.
First, as the sanitary system goes from the top deck to the engine room, more and more toilets join the system. Any one of these toilets can contribute to a problem, and everyone "upstream" of the blockage will not have a working toilet. So, if I went to a crew cabin (typically the lowest on the ship), and purposely introduced something to block