So, there's water in all the P-traps, you have no visible leaks and the pipes are free of clogs. What next?
It seems natural to assume that the toilet would be the obvious source of any sewage smells, but if there's water in the bowl, chances are the commode is not the problem. This is because the toilet water acts as a smell barrier -- just like the water in a sink's P-trap. But if the bowl doesn't fill up as it should, the problem could be a broken seal. When there is no caulk around the base of the toilet, water and urine can seep underneath and water that gets stuck in crevices and doesn't dry will grow bacteria. This bacterium can often cause a foul odor if left unchecked [source: Angie's List]. This is an issue that Patrick encounters frequently, noting that that it's easy enough to solve by adding a bead of caulk around the bottom. Sometimes it's also necessary to caulk the bolt holes because smell can leak through there, too, he says.
The wax ring, which is installed with a toilet to seal the drain and prevent water seepage, can be damaged if the toilet bowl is loose. This can result in water leaks and sewage smell. So, you should check to see if your toilet bowl is loose or wobbly – if it is, you can reset the toilet with a new toilet ring [source: Angie's List].
Occasionally, the problem is actually coming from somewhere else, even though the smell itself is inside the bathroom. For example, a roof vent blocked by a bird's nest, leaves, or snow and ice prevents fresh air from coming into the plumbing system and preventing the sewage system from venting the way it's supposed to. It can be tricky to distinguish between a blocked drain pipe and a blocked vent, so homeowners often spend plenty of time focusing their efforts on a single pipe. A few telltale signs (in addition to the sewage smell) that a blocked vent is actually the culprit are that all of the drains in the home are slow to drain, and that water makes gurgling noises or bubbles up when trying to drain [source: Jim Dhamer Plumbing and Sewer, Inc.].
A vent pipe that's been improperly installed, cut or cracked can also send offensive gases into your home. A cracked vent pipe can be even harder to track down, since the break is probably hidden somewhere within your walls. Fortunately, a plumber can locate a vent pipe leak with a device called a smoke machine, which fills the drain system with a harmless visible smoke. When the smoke finds its way out, the source of the leak is obvious [source: American Leak Detection].
Although some of the fixes are done easily enough by the average homeowner, you should evaluate your comfort and skill level before tackling a project like this. If you're handy, you could take care of cleaning drains or perhaps replacing a toilet's wax ring. But if you're not comfortable doing home repairs, or you're not sure of where the smell is coming from, it might be best to hire a pro.
Originally Published: Jun 19, 2012