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127

I noticed that when my washer drains, the toilet bowl in my laundry room bubbles from the displaced air in the sewer line. No, the sewer line isn't clogged, I've checked. This sometimes siphons all the water out of the toilet bowl, allowing sewer gases to escape until I next flush the toilet to refill the bowl and reestablish the water seal.

This toilet isn't the lowest sewer connection in the house - I have a drain in my basement that's lower and doesnt run into any siphoning issues. None of my toilets on higher floors exhibit this issue.

Any idea what's causing this or how to prevent it?

I noticed that when my washer drains, the toilet bowl in my laundry room bubbles from the displaced air in the sewer line. No, the sewer line isn't clogged, I've checked. This sometimes siphons all the water out of the toilet bowl, allowing sewer gases to escape until I next flush the toilet to refill the bowl and reestablish the water seal. This toilet isn't the lowest sewer connection in the house - I have a drain in my basement that's lower and doesnt run into any siphoning issues. None of my toilets on higher floors exhibit this issue. Any idea what's causing this or how to prevent it?

(post is archived)

[–] • 4 pts

The water exiting the washer is fully occupying the drain line. Passage of the water displaces (pushes) air in front of the flow, and creates a slight vacuum behind it. If the vent stack serving that line is insufficient (too narrow), occluded or missing, the vacuum created in the line impacts other lines that are connected to it.

If this is a sudden occurence, your vent stack was recently impacted. If it has been happening since forever, your stack is insufficient or absent. Check for the presence of and blockages in your vent stack. Get a plumbers snake and a flashlight and climb on the roof. Look down the stack to see if a blockage is visible. Snake to remove, or just generally snake the shit out of it for as far as your snake can reach. Bring a couple gallons of water with you to help flush the blockage further down into a larger pipe.

Caution: Keep a firm grasp on your snake - or tape a big wad of rags on the end so it doesn't inadvertently all slide down the drain. Neighbor did this years ago, and had to call out the pros to retrieve it.

[–] • 1 pt

Thanks for the detailed response, it makes sense. I already scoped the sewer line, but hadnt thought to check the vent. I'll dig my scope out and check it. This has been going on for years and I only caught on to why the toilet bowl would "randomly" be bone dry through dumb luck of walking into the laundry room while the washer was draining.

[–] • 4 pts

You have a blockage at the end of your sewer/septic line. The vacuum created as your washer water exits the system activates a “flush” on your toilet.

[–] • 2 pts

I know someone that had a similar issue and this was the cause. YMMV though.

[–] • 3 pts

one of your vent risers is clogged with something.

[–] • 1 pt

As others have said, you have a vent blockage. This is not a clog issue down the line, it is insufficient air admittance.

[–] • 1 pt

That makes sense. I scoped the sewer line (all good), but didnt think to check the riser.

[–] • 0 pt

Please let us know what your end result and solution is!

[–] • 1 pt

Make sure you don't have kikel sewer rats trying to climb through the drains.

[–] • 1 pt

My sewer line is upwards of 100' long, if a sewer rat climbs it I'm giving it a Shawshank medal for sheer perseverance.

[–] • 0 pt

Do you have an air gap where your washer drains or is it directly plumbed into the drain?

[–] • 1 pt

There's a small air gap. I hadn't considered plumbing it directly, that seems like it'd be a noisy mess that'd drain about as poorly as modern gas cans.

[–] • 0 pt

It is good it has an air gap. I was thinking lack of one could be the problem.