If toilet isn't sitting pretty, air can be pretty foul; faulty seal can let gas escape

The toilet in the house I just moved into is loose on the floor. How hard is this to fix?

Also, there is a sewage odor in the bathroom whenever I take a shower or the wind blows, but only during those two times. Is this somehow connected to the high iron content in the water?

—G.S., Kalamazoo


Iron-rich water can indeed produce foul smells. The cause is harmless, though unpleasant, bacteria in the water supply. However, most people describe the odor as “sulfuric,” or resembling rotten eggs, not sewage. And, if it were occurring in this instance, you would probably smell it at every fixture in the house, not just in the bathroom.

Zolton Cohen

The odor is usually stronger in the hot water supply, and windy conditions outside would not affect whether or not it appeared.

But the loose toilet and the odor problem could be connected. There is a wax ring under a toilet that, during installation, gets squashed down to create an airtight seal between the underside of the toilet and the top of the flange on the drain pipe. As long as the toilet is rigidly fixed to the floor, the wax stays intact and effectively seals sewage odors from traveling up the pipe and into the house.

If toilet isn't sitting pretty, air can be pretty foul; faulty seal can let gas escape

But if the bolts holding the toilet to the floor corrode and break, or the nuts that hold the toilet to the bolts loosen, or something else liberates the toilet from its mooring, the fixture can start to rock from side to side. That’s bad news for the wax ring.

Once the ring gets compressed by the rocking, it has no ability to re-expand to fill the gap between the underside of the toilet and floor flange. The toilet may not leak water during a flush (many wax rings incorporate a plastic funnel-like transition piece that effectively prevents leakage even if the seal is breached), but foul-smelling air is free to travel from the drainpipe into the house. The odor is distasteful and, because it can contain pathogens, it is also unsanitary.

The smell occurs when someone is showering because the water going down the drain displaces some of the air in the drainpipe. That air usually vents harmlessly above the house roof through the main plumbing vent pipe. But, because it now has a path of least resistance nearby, it exits through the gap under the toilet. When wind blows across the top of the roof vent pipe, it creates negative pressure inside the pipe, which sucks air up from the sewage system and through the gap.

The fix is to take the toilet off its defective mounting and replace whatever hardware has failed. After that, reset the toilet with a new wax ring (about $3). The old one cannot be reused.

If the toilet is older than 10 or so years, and especially if it is a 3.5- or 5.5-gallon flush model, it is worth replacing with a new low-flow unit. Toilet manufacturers have put a lot of time and effort into developing fixtures that use very little water and yet still flush completely — in contrast to some early low-flow versions that were not effective.

If replacing or resetting the toilet doesn’t fix the problem, look for a cracked, disconnected or otherwise compromised main plumbing vent pipe near the bathroom. Although rare, these defects can produce odors like the one you described.

Zolton Cohen is a Kalamazoo-based newspaper columnist and former American Society of Home Inspectors-certified home inspector. Write to Zolton B. Cohen, Around the House, P.O. Box 2007, Kalamazoo, MI 49003.

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