I have a customer that is on septic, but supplied with water from the city. The master bathrooom shower has a really bad smell when the water hits the drain. The bathroom was remodeled 2 years ago, and the shower and toilet plumbing were both redone. It is not a build up in the drain and bleach and vinager didn't do a thing. Does anybody out there have any idea what could be the problem? Somebody told me that they though that the trap was too low, another said the shower pan is retaining water. Do I really have to tear out the shower, drop the trap to increase the water lock, and then put in a new shower for the guy? :confused: That is a very expensive fix...
By the way, I looked in the attic and there is proper venting for the underground. Any help would be greatly appreciated.

I am taking a big guess but based on what you say I think the drains were not properly trapped during the remodeling. The flushing of the toilet pulls water out of the shower trap letting sewer gas back in.

Didn't notice anything when flushing the toilet...