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Plumbing Bathrooms

Sewer smell from drain but only when water is running?!

2 years ago

When the shower is on, sewer smell comes up from the drain. I can't figure it out! Clues:

It only happens when the water is running.
No other drains (bathtub, sinks) in same room or elsewhere do this.
It's a rural home with septic system, about ten years old.
For years, the shower was very low flow but when I got here, I fixed the flow (a defective washer was plugging the shower head supply hose) and I think that's when the smell started.
The shower drain pipe goes straight down for about 7 feet, then there is a trap, then a horizontal run where it joins other drains on the way out.

Any ideas? I am stumped!

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Comments (5)

Liz H
2 years ago
When was the last time you had your septic pumped/inspected?
Moe Rubenzahl thanked Liz H
functionthenlook
2 years ago
My kitchen sink does the same thing at camp. It is only the sink. About every 4-6 months i use the baking soda/vinegar hack and it is fine. We had the septic pumped this summer and the honey dipper said it wasn't near full yet.
Moe Rubenzahl thanked functionthenlook
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Did anyone inspect the vent pipes to make sure they were installed correctly? Try also posting this on the Plumbing forum. I found this on another web discussion site: "It may be that you have a leak in the sewer stack, and that the expansion with the hot weather is whats causing it. Cold weather contracts various things and may seal it up again. I too am the type that I can smell things in parts per billion (reason why a lot of times, the Superintendent would ask me how the plant was doing, because I was the first to be able to detect things at the Waste Water Plant). Another possibility is that something is in your attic and its coming down through cracks in the ceiling or through the walls, in your bathroom, (dead squirrels or some critter). Now, make sure, to check your TRAPS in the shower or bath. its possible, that you have a plugged up soil stack, (though the plumber should have found this, if he checked the roof), and that when the temperature gets warm, or something happens outside, it sucks down the water from the traps in your bathrooms, (like when you use your sink in the kitchen and it creates a vacuum and draws down the water from the traps if the pipes aren't big enough...)"
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Seabornman
2 years ago
It's possible you are smelling the gunk that builds up on the sides of the pipe before it gets to the trap. You'd need a high volume of water to siphon out the trap. I assume that line you think goes to sinks is properly vented.
Moe Rubenzahl thanked Seabornman
Moe Rubenzahl
Original Author
2 years ago
Good suggestions, helps me think this through.

Because the smell is only when water is running in that drain, I don't suspect gunk on the sides of the pipe. For same reason, I don't think it's the septic. A vent issue is possible, or it's because of the very long drain above the trap, causing enough pressure to gurgle back through the trap, because of venting inadequacy. Those are my thoughts....
HU-867564120
2 years ago
I would suspect that your venting is the issue. The water that goes down the drain will displace the sewer gasses. If the sewer gasses don't have any where to go (as it would with a working vent), they will go the only other place that they can go, up through the drain that the water just went down.

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