I am getting a dirty water smell in my den and kitchen. I am also getting a small flying insect (i think they are sewer flies. I had a plumbmer video survay my pies when this happened a few years ago and he found a break in the pipe in my slab. He rerouted the existing pip by plugging it and ran a new pipe around the house into the main line. This fixed the problem and the smell went a way. Now the smell is back. Any help would be appreciated.