smell in shower drain

Hi,
We just bought a home that was built in 1992 with several showers in it. The one on the main floor was connected to a guest bedroom and rarely used. This is my 15-year old son's room now and he showers every day. There is a smell coming from the shower drain. It's not a sewer smell, more like a musty locker room type of smell. I tried pouring bleach down the drain several times. I had a plumber out and he looked at the pipes and said everything visible was working properly. No leaks unless they were in the walls. My husband took an outlet cover for a phone jack close to the shower off the wall to look inside and saw no moisture or moldiness. We are baffled and the smell continues to get worse. There is a water softner and sump pump in the basement (directly under his room). Could the smell have anything to do with either of these? Please help!

If you smell mildew, it is probably present somewhere. Seldom used shower? Look there. Could be in the door frame where water will sit for a long time. We have a basement tiled shower that is rarely used, it smells like mildew - I blame it on the door but too cheap and lazy to put a new one in. I want to demo the whole shower but it's not at the top of the list (yet ).

Is this a tiled shower? It is quite possible to have one that doesn't leak that can get smelly. This only happens if it is not installed per the tile council of america guidelines (which is code many places). It is not uncommon to install the liner flat on the floor rather than on a presloped floor. If this is done, any water that gets below the floor of the shower (and it will no matter what you do), will accumulate and eventually smell like a swamp rather than hit the sloped liner and be directed to the drain. If that is the case, there isn't much you can do other than redo it. Grout sealer and ensuring the caulk is intact helps, as would drying the shower with a towel after you finish your shower will help, but not solve the problem. If you want to understand the approved way to build a shower pan, take a look in the 'liberry' over on www.johnbridge.com