Our front-load washing machine has a problem where sometimes it really smells of sewer gas. This only happens occasionally, and we can only smell it when the door is open. We usually leave the door open so that it can dry out and not get moldy.

Presumably this happens because a trap is somehow losing water (maybe through evaporation?). There's a nearby bathroom sink that also has the same problem but I can just run water for a couple seconds to refill the trap. I can't do that with a washing machine. The washer and dryer are also installed in a narrow closet so I don't have easy access to the drain plumbing to see what's going on. Here's a photo of what I can see. That looks like hot and cold supply, and I'm fairly certain there's a drain going out the base on the back as well.

Any idea what the likely cause of the problem is and what it would take to fix it? I want to go in with a plan before attempting to pull the appliances out.

Edit: As a reference point, here's what's under the sink with the same problem.

  • what is behind that wall where all the pipes come from
    – Traveler
    Commented Sep 5, 2023 at 23:10
  • Bathroom sinks are usually on top of cabinets. Their back walls are usually hidden from view, so patching well/perfectly is not as important. Just an option to fix the problem.
    – crip659
    Commented Sep 5, 2023 at 23:27
  • Installing laundry hookups like that is a form of insanity.
    – kreemoweet
    Commented Sep 6, 2023 at 4:58
  • @Ruskes The left wall is a closet on the other side. The back side, where I believe the drain is, is a brick wall to our neighbors.
    – David K
    Commented Sep 6, 2023 at 14:34

2 Answers 2


Losing the water in the p-trap is usually a sign of a malfunctioning or non-existent vent. As others have said, you need to uncover the pipes to see the layout and with that identify the problem. There are many solutions, depending on the cause.

Without opening up the walls, at least I'd check if the sink p-trap is full of water (just disconnect it and see if water comes out), or if the laundry machine is discharging into a p-trap, or if it's just a straight pipe inside of the wall, or an illegal s-trap.

  • I just edited to add a photo of what's under the sink too. I don't see a vent there, so there's probably not one on the washer either.
    – David K
    Commented Sep 6, 2023 at 22:42
  • @DavidK The vent would be inside of the wall.
    – Cheery
    Commented Sep 6, 2023 at 22:58
  • Ah, gotcha. Unfortunate that I can't see that without breaking open the wall.
    – David K
    Commented Sep 6, 2023 at 23:49

I think you know what the problem is: "There's a nearby bathroom sink that also has the same problem but I can just run water for a couple seconds to refill the trap". I think you're going to have to pull out the appliances before making a plan. You'll need to investigate the drain connection and possibly remove some drywall to see exactly what you have. Before doing that, you could get a snake inspection camera and run it down both drains to see if it shows any problems.

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