I have a bad sewage smell when flushing all toilets in the house. The house was built 2 years ago on a slab. The toilets flush normally, water levels are good, only once did we have a clog which was remedied by a normal plunger. Each time we flush we smell the sewage. No smell comes from other pipes in the house only the toilets. Any suggestions would be great, I am about to call a plumber. I am suspect of the builder and the plumber they hired when building the home to begin with.