We live in a two story colonial home - just moved in 5 months ago. I noticed that one of our second story bathrooms often gives off a sewer smell. The other day I opened the lid to find foul backup - dirty water and paper. This toilet is almost never used. It obviously is getting backup from somewhere. We are on a public sewer line and we have very hard water. Could the hard water have damaged the sewer pipes and caused this backup? Any recommendations on what to do or how to diagnose the problem?
-kcast

I think it would be almost impossible for you to have a back up one the second floor in one bathroom without having a problem in another bathroom on that same floor.
Also I would think it impossible for you to have a backup from one of the commodes and the ground floor. So I think you need to do some questioning and see if maybe someone may have used that bathroom and you didn't know it.

Kcast - Let me ask you a question : Does your house set down say at the bottom of a hill ,and have other houses a lot higher then yours? Un less the main sewer line was stopped up and you are at the lowest point of any one else's house it's not quite possible, and that's the only one that way ,and its on a second floor. Now that toilet might have a stoppage between floors, as far as a sewer smeel , ity was probably comeing from the full toilet . ( I AGREE WITH - LETME TELLU ,AND ) have you tried flushing it to see how it goes down and listen to see if you hear a gurggling sound I hope this helps you ,if it does rate my answer below:: GOOD LUCK & GOD BLESS::: F.B.E.