How do I stop an intermittant sewage smell from all of the drains in the house?

Answer 1

First it is necessary that you understand the source and cause(s). Sewage smell is caused by decomposition of sewage throughout the entire system, including the sewer mains. Any opening in the sewer system will allow vapors to escape. As a matter of fact, the Plumbing system vents sticking up above your roof are there to vent any such gasses at a height which is considered to be far enough away from human activity to not interact with people. If you were to remove a toilet, a lavatory, or sink from the drain system, leaving an open pipe end, those sewer gasses would enter your home. Even with those fixtures in place, still gas could enter through the drain opening, EXCEPT that codes require ALL DRAINS [including floor drains buried in a concrete floor slab] to have what is called a "P" trap installed at the drain outlet of those devices. The p-trap is so named because it resembles the letter "p" lying on it's side such that the curved part is downward, creating a "u" shaped loop which will catch and hold [trap] the last bit of water draining through it. In effect, this creates a "plug" of liquid in the drainpipe, which prevents the sewer gasses from backing up through the fixture drain into the house. Now, with this knowledge, we can approach the question of how intermittant odors occur, assuming there are properly installed p-traps in all drains in the house. IF there is not a p-trap, or it's not properly installed with the curved loop down, so as to trap water, then the fix is to reinstall it properly. However, since you use the term "intermittantly," suggests that there are properly installed p-traps and there must be another cause. Occasionally, where you have plumbing fixtures that are seldom used, the plug of water filling the p-trap will evaporate, leaving the p-trap open thus allowing the sewer gasses to enter the house. Each time water is run through a drain, the last of the flow refills the p-trap. I suggest that for any fixture drain which is not used at least monthly, you intentionally run water through the fixture every two weeks. This should preclude evaporation of the plug, and prevent entry of sewer gasses. There is one other possibility of sewer gas passing through a fixture drain, even IF the p-trap is properly filled with liquid. If the roof sewer vent pipe is blocked or restricted [by for example, like a bird nest at the opening, or a blockage due to accumulation of spider webs and trapped tree leaves in the vent], then when a toilet is flushed, or a bathtub full of water is drained, then the quick, heavy flow of water into the sewer pipe system displaces the atmosphere [air and sewer gasses] in the system faster than the restricted vent system can handle. In this situation, it is possible that the pressure build up of sewer gasses, exeeds the strength of the p-trap water plugs to resist. Then the sewer gasses will bubble up through the p-trap water plug into the house. Another thing which can cause the same backup through the liquid filled p-traps are large, but incomplete restrictions [partial clogs] downstream in the sewer pipes. Thus, you stop intermittant sewage odors inside a house by finding, and correcting the defect which allows the sewer gas to escape the sewer system.