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Clogged soil stack could be cause of burping toilet

House Doctor | Gary Dymski

October 20, 2005

My home is three years old. I hope you can shed some light on a mysterious plumbing problem with the toilets in my upstairs bathrooms.

One bowl releases a bubble of air every time it is flushed, causing water to splash over the seat and rim. Whenever the toilet is flushed in the other bathroom, a very loud banging can be heard from the pipes in the wall in the room below. This sound is not caused by the rush of supply water; it is drain-related. Besides, I already have added an anti-knocking device to the supply line.

The noise happens only if the bowl contains paper or solids when flushed. Two plumbers have been no help.

Frank M., Huntington

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The system of large-diameter pipes that carries water and waste to the sewer or septic tank is called the DWV system (drain, waste, vent). This system has three components: Drain lines collect water from sinks, showers and tubs; waste lines carry waste from toilets; and vent lines exhaust sewer gasses and provide the necessary air pressure so waste will flow freely. Normally, a toilet will burp in this manner because the soil stack, a line that carries waste to the main drain, is clogged. I also wonder if your vent line, which exhausts gasses to the roof, might not be plugged or partially clogged in some way. I would suggest to the next plumber that he examine the vent line to the roof. All waste lines in the system should have clean outs, a Y-shaped fitting in the line that is capped off. In the event of blockage, the plumber can snake out the line.

Even though your house is new, the installer or plumbing contractor might have missed a step in the installation that allows each waste line to be vented properly. Call the builder and request that he provide you with the name of the plumbing contractor who worked on your house. I'd give that contractor a call and plead your case. In my opinion, the contractor should respond promptly. If it is an installation-related problem, the work would be done without charge. If you don't get a positive response from the contractor, I'd have a reputable plumbing service thoroughly inspect the system.