Well, at least I'm not the only one with such a problem with ancient plumbing, as proved by “Flushed – How the Plumber Saved Civilization Proves”. W Hodding Carter is funny and charming and turned this book into a really easy reading experience.
The journey starts from the earliest times, spends a lot of time in ancient Rome, moves on to worse experiences in the overcrowded London a millennium and a half later, and ends up with our modern facilities. Everything is spiced up by the author's attempts to recreate ancient toilets in his own backyard. (He did it so we don't have to.)
Flushed is funny, relaxing, and kept me awake on an airplane trip, which says a lot.
Don't buy it if you're an expert in plumbing or the history of plumbing and you're looking to expand your knowledge into what's already your area of expertise. It's not technical, and doesn't bring anything new. (Even if it's not a technical manual on how to build your own ancient Roman plumbing system, it could have benefited from some pictures and illustrations – which, sadly, are not there.)
Also don't buy it if you're a history buff and you're going to frown upon every little inconsistency. The sources are secondary, at best, and the accuracy is questionable.
If you're everybody else on the planet, go ahead and read it. You'll treat your toilet with much more respect after that.