I dont't know if anyone here has seen History Bytes. It's on the history channel however I believe it is only on the Canadian version. I know it from the newsgroups. It is very good historical satire. Anyway in one episode Martha Stewart in roman times is talking about the benefits of Portugese urine for mouth wash. The stronger the better.
Now since the show is based on history I quickly did a google on urine mouthwash. Sure enough, the Romans used it.
I guess no matter how bad it tastes, I'd stick with Listerine.