Published on January 14th, 2015 | by Henri


Sewer smells come from floor drain

Q. There has been a very unpleasant, sewer-like odor coming from the floor drain in my utility room. We have a 19-year-old tri-level with a basement (4 levels total), and the utility room is one level up from the basement. This drain runs from the utility room, underneath the garage floor, through the basement, then out the basement side wall.

Nothing ever drains into this drain, so the water just sits in the trap and has become very dark brown-grey and mucky looking. Sometimes there are small pieces of debris floating in there (don’t know what it is).

I poured a quart of hydrogen peroxide down the drain, allowed it to sit overnight, and flushed with water. After repeating this process the next day, the water in the trap was a nice clear color and the smell was gone. By the way, the water drains very freely down the drain; there does not appear to be any blockage.

However, after about one week, the smell is starting to come back and the water is starting to look brownish again. My questions are as follows:

  1.     Any idea what could be causing this odor? (it’s not a dry trap; there’s always water in it, albeit smelly and brown).  My theory is that the drainpipes from my toilet(s) might be tied into this pipe, and perhaps this part of the pipe has a “negative” slope, (due to settling?), and some of the toilet waste is sitting at that end of the drain pipe (in the utility room). In other words, water and some partial waste is sitting in the trap as well as in that run of the pipe.
  2.    Do you have any “preventive maintenance” recommendations to keep my drains (tubs, showers, sinks, etc) nice and clean, and odor-free?

Fortunately the only one that smells is the drain in the utility room, but I would like to “stay ahead of the game” with the other drains. I was thinking about getting a plumber to perform a video inspection and perhaps determine what the problem is, but I would really appreciate any input you might have.

A.    I doubt that the smelly and dark-colored water is from the toilets; if it were, you would see some gurgling when the toilets are flushed, among other problems. Any water standing for a long time in a trap is likely to turn a dark color from the rusting of the cast iron trap – and to have floating scale, and start smelling.

Inflatable Pipe Plug

Inflatable Pipe Plug

If this trap is not used and you have never had a problem with leakage from your washing machine, you may want to consider getting an expandable ball-shaped plug that plumbers use to block sewer gases from coming out; it won’t change the color of the water in the trap but it will block the smell. Buy one in a hardware or plumbing supply store. In case of need, it is very easy to deflate it and remove it.

Having your pipes videoed seems somewhat drastic under the circumstances; the problem does not seem to be that serious. The best preventive measure I know of to keep drains open and sweet smelling (if there is such a thing) is to pour a solution made of hot water and Super Washing Soda in the drains on a regular basis; follow instructions on the side of the package.

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