Eliminating Drain Smells

Q: How can I stop the smell of sewer gas that mysteriously comes out of our toilet several times a month? It seems to happen when I’m washing a lot of clothes in the nearby laundry room, or when several people take showers right after each other. Any ideas?

A: It sounds to me like the drainpipe leading from your toilet might not be vented properly. Here's why I suspect this. All toilets, sinks, showers and bathtubs are connected to drain lines, and these would allow foul smelling sewer gases to enter your home if it weren't for an S-shaped bend in the drain system that always holds back a little bit of water. This is called a "trap" and the water in it seals the drain and prevents sewer gas from coming inside your house. Problems arise, however, when air isn't admitted properly into the drain line as wastewater rushes out. When this happens, suction can develop in the drainpipe, drawing enough water out of the trap to ruin the sealing action. The improper draining of nearby plumbing fixtures (like the laundry sink and shower at your house), can also draw water out of the traps of other fixtures, such as your toilet. The vertical plumbing vent stack that goes through the roof of houses is designed to admit air into the system, eliminating problems with dry traps. But sometimes, internal drainpipes aren't installed properly to allow this air to do its job. In this case the best solution is to install an internal plumbing vent. This is a one-way air valve you install on the end of a vertical pipe spliced into the drain near the offending area. You need to make this new vent as tall as possible while remaining hidden. Installed correctly, interior drain vents work very well in cases like yours.