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I had a previous question about my toilet leaking in my washroom. For some strange reason, the washroom has a strong, persistent stink despite everything we do to remove it. What are the possibilities to investigate? Could it be mold?

We've tried:

  • Turning off the toilet water supply, flushing it to empty
  • Emptying the garbage
  • Cleaning the toilet bowl with strong, apple-scented cleaner
  • Spraying those washroom scents until the smell is gone

Despite all this, the stick returns, persistently. I don't think it's getting worse every day, but it's bad enough to keep us away from using that washroom. (We haven't used it in weeks, and since spraying and cleaning it; the smell returned in a day or two.)

I really hope it isn't mold; but what should I look for in terms of possibilities?

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So putting water in the tub and sink didn't help? Is doesn't have a floor drain does it? –  BrianK May 16 '11 at 17:37
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3 Answers

up vote 11 down vote accepted

Our second shower sits unused for weeks and sometimes months at a time (daughter moved out.) About a year ago, a horrible smell started emanating from that bathroom - after many unsuccessful attempts to kill the smell, I finally realized that the P-trap under the shower floor must have dried out, allowing sewer gas to rise up through the drain. I ran a couple of gallons of water, and the smell went away. I run that shower for 30 seconds or so once a month, and the smell has never come back.

So: any unused plumbing fixtures in that washroom?

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Absolutely an unused tub in there. I'll try the gallon of water. –  ashes999 May 15 '11 at 23:18
    
I just noticed in your original question "Turning off the toilet water supply, flushing it to empty" - as you may have already guessed, this is a terrible idea! You need water in every P-trap in the house. Meanwhile, hope things are working out. –  MT_Head May 15 '11 at 23:37
    
This is simply a precaution to prevent further leaking. I've since replaced the supply line and re-activated the water flow. –  ashes999 May 16 '11 at 12:25
    
Excellent. Didn't mean to nag; just wanted to underscore that the very same problem (sewer gases coming into the house) can happen via an empty toilet, too. –  MT_Head May 16 '11 at 16:41
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I heard a really great tip for seldomly used fixtures: add a tablespoon or two of cooking oil to the drain. That layer of oil won't evaporate, and it helps prevent evaporation of whatever water's in the P-trap. I'm doing that in an un-occupied home now. –  pboin May 17 '11 at 11:20
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I'll second MT_Head's thoughts that you're smelling sewer gas, but give you a second location that it could be coming from. The wax seal under your toilet could have failed. To fix this, you'd have to:

  1. Shutoff the water
  2. Drain the toilet and tank
  3. Unscrew and remove the tank
  4. Unscrew and lift the base
  5. Remove the old wax seal and clean as best as possible. You should also clear away any old caulk at this point. If this takes a while, it doesn't hurt to shove a plastic bag or something into the drain to avoid sewer gases, just don't leave it in there at step 7.
  6. Place a new wax seal on the bottom of the toilet with enough pressure to make it stick, make sure that the gasket/flange/whatever the right name is, that this points away from the toilet (into the drain)
  7. Carefully place the toilet back over the drain hole, doing your best to line up the two bolts on either side before the wax seal makes contact
  8. Double check that the toilet is lined up with the wall
  9. Press down on the toilet base as evenly as possible until it makes contact with the floor. You don't want to lift up in any way at this point. If there is any separation between the toilet and wax seal, you can get gases escaping. Avoid too much rocking back and forth.
  10. Replace and hand tighten the bolts on base of the toilet. Over tightening can crack the porcelain. Use the socket without the wrench for a better grip. And then give it maybe a quarter turn with the wrench, but be very gentle.
  11. Replace the tank, same rules apply when tightening the bolts.
  12. Reattach the supply line. It doesn't hurt to double check the washer at this point. If it's a large plastic nut with wings, hand tighten it. Otherwise, be gentle with the wrench.
  13. Cross your fingers and turn the water back on.
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This seems unlikely, given the lack of any leakage around the base of the toilet. –  ashes999 May 15 '11 at 23:18
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The fact that the stink returns persistently means that you have (or recently had) a leak. You should check:

  • Toilet drain - do you have access underneath? If not, do you notice any staining or peeling paint? This is unfortunately the most likely problem given your previous issues.
  • sink drain - same question
  • Shower/tub: check the drain, overflow, valves, and shower head
  • Exhaust fan/duct - does it work well? Could moisture have collected inside it?
  • Supply lines - probably not as likely as a drain problem, but a leak in a wall or floor could make good conditions for mold/rot
  • Drain vent - an obstruction here could potentially lead to bad smells entering your bathroom instead of being properly exhausted outside
  • Leaks around tub/shower - if the water sealing around your tub or shower has failed, water could be soaking into the walls/floor. Check for loose tiles, missing caulk, or water exiting the shower area (e.g. due to a badly positioned curtain). In particular, look for any areas where water might pool.

Unfortunately, unless a leak is obvious or you have easy access to the plumbing lines, investigating this may be pretty destructive. Prepare to open up walls and ceilings. Despite that, it's important to look into it soon -- this is the sort of problem that only gets bigger with time.

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I don't have the tools or skills to do this. What's plan B? No peeling paint or any other visible leakage anywhere that I can see. –  ashes999 May 15 '11 at 19:44
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