Sewer gases when washer empties

I have an issue that I can’t provide an answer to. When the washer drains ( a new high efficiency model), there is a strong odor that seems to come from the basement floor drain and I am assuming is ‘sewer gases’. This only seems to happen if the washer has been idle for a few days. A second load on the same day does not produce any odor?
Anyone having an explanation would be greatly appreciated.

Happy inspecting,

Is the basement floor drain trap dry? Maybe the floor drain trap has a crack in it and or is evaporating. Maybe the floor drain trap is getting some water from the clothes washer, sealing the drain from sewer gas. If the trap has a crack in it the seal will deplete and the gas smell could come back hours later.

That was the first thing I thought of so I check the drain before the washer is used and it always has water in it???
The smell only shows up after the first load drains and is never there when the washer isn’t being used. could the discharge from the high efficiency washer be stronger and actually create a temporary air gap at the floor drain that lets some gases in do you think?
Thanks for your help.


Oh, there is also a rough in for a bathroom there. Is it possible the smell is coming from one of those rough-in pipes? They are all covered but they don’t have airtight seals.

Could be?
You could do a smoke test to be sure.

Try putting 2 parts vinegar to one part baking soda down the drain. It could be just bacteria growth.

hmmmmm…sounds like a grade school volcano experiment to me!

Is the clothes washer on the same floor as the floor drain? Sharing the same vent? Could be creating a temporary siphonage drawing the seal out of the floor drain but that doesnt explain how the floor drain trap is re-sealed.

Is it possible that the washer is not trapped or the trap seal can’t form making the washer drain act like a vent. When the washer is run it rinses down the pipe forcing gas out through another vent. Just a thought.

How about an “s” trap in the washer drain line?

Washing Machines do not completely drain during the pumpout cycle. The water that remains in the Laundry Washer can become stagnant if the washer is not frequently used.

It is not the sanitary drain that is causing the odor. It is the Appliance.

Washer is trapped with a ‘P’ trap. The odour didn’t show up until about 5 or 6 months after the washer was brought into use so maybe stagnant water in the appliance is the problem. I will investigate that. Thanks to all for the help. I’ll let you know if I get it solved.


I know if I close the lid on washer, and it’s several days before I do laundry again, when the washer lid is opened, it smells sour inside. I haven’t noticed any further odors, tho.

Is there an air gap where the hose goes into the drain, Linda?