Recently suds spouted from inside my toilet like this:

enter image description here
Click images to embiggen

enter image description here

The plumber concluded that someone on a higher floor used too much soap, but plumber can't pinpoint which.

How can I foolproof my toilet from all these suds overflowing again, particularly when I am traveling away for business?

Anyone got better ideas than buying quick dams, flood bags, barriers?

  • 1
    That much, second hand! That's like someone used washing up liquid in a dishwasher, or hand washing detergent in a washing machine (the latter is an easier mistake to make). You might have been able to smell the difference. I doubt there's much you could do; while a couple of drops of cooking oil on the surface of the water might help, making a habit of it risks clogging the stains with fat buildup.
    – Chris H
    Feb 9 at 8:07
  • 2
    Clearly there’s a constriction downstream that management needs to deal with, but I’m idly wondering if a silicone mat as a gasket and a somewhat heavy weight on the toilet rim would slow the suds in the meantime. (I’m assuming it was just suds — not full on water coming over the rim.) Feb 9 at 14:32
  • 1
    I honestly don't think any of the dams or barriers you're looking at would do much. The suds would just flow right over the top of them.
    – FreeMan
    Feb 9 at 15:01
  • 2
    You have a problem below your toilet that is stopping the sewage from draining out into the sewer properly. It backed up and came out your toilet. If you stop it coming out your toilet it will just come out somewhere else. If you block up all of your drains it will come out your neighbour's drain. Be very glad that it was suds and not "actual" sewage. There have been other instances where a sewer blockage has made the upstairs neighbours' poo overflow from people's sinks, toilets and showers. The building needs to fix this.
    – user253751
    Feb 9 at 18:25
  • 1
    Some bad advice :-) : Using eye protection, dissolve 500 grams / 1 pound of caustic soda / sodium hydroxide / lye / .... in a half bucket of water and pour into the toilet. Use more water if it is not enough water to dissolve. Wash hands and other skin as needed. DO NOT get this in your eyes. || That will greatly help remove obstructions further 'downstream'. Repeat if needed in a few days. || This will work both on tree roots and on eg fat accumulations. || All care, no resposibility. I'd do this myself. Feb 11 at 9:51

5 Answers 5


You'd have to plug up the toilet exit somehow. Plumbers use inflatable "test balls" to plug drains, they are available at many of the larger hardware stores and certainly at plumbing supply outlets. It's just a rubber ball with a length of tubing with a Schrader valve on the end. Requires a standard air/bicycle tire pump to inflate. Get the right size, which would be something like 2-3 inches.

  • 4
    Curious, would plugging the toilet just make the suds come out of the sink or tub?
    – RMDman
    Feb 9 at 12:52
  • 4
    @RMDman probably, unless their drainage was separate - which it probably isn't given the occurrence in the first place (unless someone cleared a blocked toilet with loads of foaming detergent and hot water)
    – Chris H
    Feb 9 at 13:49
  • The sewage outlet and the sink waste should ALWAYS be separate. That foam comes from somebodies toilet - its not clean water. Feb 11 at 19:43
  • 2
    @JeremyBoden they join soon enough in pretty much any system, always before it the waste pipe leaves the premises. That's what products like this are for
    – Chris H
    Feb 12 at 13:33

We had this exact thing happen in our single-family house, in the basement bathroom. Turned out to be roots in the sewer line. So you may have a restriction someplace downstream of that toilet, which results in the sewer line developing enough pressure (which it should never have) to force foam backwards through the trap in the commode. I suppose it could also be a plugged vent, although that would more likely cause gurgling and emptying traps in multiple fixtures.


I suspect there's a partial blockage in the lateral, if they only cleaned the stacks, that blockage would have not been addressed, and it may even have developed since then.

In any case:

Whatever maintenance the manager claims to have contracted is immaterial: the plumbing is malfunctioning today. What you want to do is arrange it so that the building pays for the repairs to your home. That will motivate them to fix the drainage problem whatever it is. You may need a lawyer to assist with that. As a title holder you will no doubt end up paying some fraction of the cost.

My opinion is not legal advice. I am not a lawyer.


I agree that the building operator is responsible. I'd start there.

However, as a fallback plan you could treat your toilet and other vessels with defoaming agent per the product instructions. This way, even if material is forced out, it'll simply collect in the basin without overflowing.

Shallow bowls in the sink and tub might work to contain the agent in case it's needed. You could treat just the sink trap, for example, but that may get drained away. Keeping some diluted agent in a pan would help retain it during an episode.

  • Thanks. 1. What do you mean by "treat" my toilet with defoaming agent? Don't I just pour this agent in the toilet bowl? 2. What do you mean by "it'll simply collect in the basin without overflowing." ? 3. What do you mean by "Shallow bowls in the sink and tub might work to contain the agent in case it's needed." ? Again, if I just pour defoaming agent in my sink and tub, then why need shallow bowls? Feb 10 at 21:07
  • 3
    @user1147844 I assume isherwood meant 1. pour it into the bowl, add more if you flush it away, 2. foamy water and more air gets pushed up into your toilet bowl, but the foam pops (and no new foam forms) so nothing overflows unless something is REALLY wrong, 3. if the defoamer stays in the sink trap (u-bend) and similar, nice. But if water from below pushes up, it might replace what is in there and wash away the defoamer - having some in a bowl inside the sink (etc) instead which would pop any bubbles coming up and touching it might help in that case.
    – Syndic
    Feb 12 at 6:57
  • Thanks, Syndic. You nailed all three. OP, read the bottle and act accordingly.
    – isherwood
    Feb 12 at 13:48

I agree that the building operator is to blame, but the quick solution is to plug the toilet. Obviously air is forcing its way through the trap in the toilet exit (together with some foaming agent) which means there is backpressure in the sewer, and it may eventually clog completely.

If this is for when you are going away, I suggest putting a trash bag in the toilet and filling it with water. It will be cheaper (and potentially more reliable / convenient) than an inflatable test ball.

  • 1
    @isherwood thanks for the edit. As for "defoaming" agent, that's not what I said, I said "foaming" agent, a catchall term for any detergents, shampoos, foam baths that are making their way back up the pipe from the neighbours. Water in a bag seals very well because the bag follows the contours - you get a good seal near the bottom where the pressure from the weight is highest. An inflatable usually wants to be round, which is great if your hole is round but doesn't work well if your hole happens to be an awkward shape like rectangular. Feb 12 at 18:56
  • Thanks. My mistake on the misread. Some of that would make a good enhancement to your answer, though.
    – isherwood
    Feb 12 at 19:08

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.