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The house I live in is 14 years old and is connected to the municipal water and sewage system in the Toronto, Canada, suburbs. I am on my second dishwasher. The first one was a cheapo Whirlpool, the current one is a mid-priced Miele. Nothing too fancy, but not cheap too. Both of them have the same issue: after it rains, or while it rains for a long time, the dishes and glasses/cups come out stinking of rancid fish.

None in the household was ever able to feel any odors from tap water. And we do not feel any odd smell from the sink drains or from the toilets. We never had sewage backup, knock on wood.

What was suggested to me:

  • That the drainage pipe out of the house and into the sewage could be cracked, and rainwater may be pushing sewage gases up the drain. But I would imagine the stench would be felt from the sink drains as well. We do not feel any of that. And the issue started as soon as we moved into the new house.
  • That rubber gaskets in the dishwasher have deteriorated and let wastewater stagnate in the joints. I am also having a hard time buying into this theory, as both dishwashers had this issue since brand new.

I found a workaround with the new Miele dishwasher - if I stop the cycle right after the rinse is complete and before it begins to heat and circulate air out and into the drainage, the smell is either reduced to a minimum, or not there at all.

It also helped to add about 1 cup of white vinegar to the water once the cycle fills the pan. The smell was reduced, but not removed completely.

And finally, the smell was reduced significantly after installing the whole house filter from Vitasauls. The smell was horrible very often before that, and now it is noticeable only after it rained for a while.

I have a suspect, but that is inconclusive: the pleated drain hose of the dishwasher sounds like a perfect spot for breeding bacteria which arrives with the tap water, contaminated during the rain. But what can I do, if they all come with pleated plastic hoses?

I know that this is a very widespread problem with no one-size-fits-all resolution, but hoping for suggestion from anyone who experienced the same.

The picture below is very similar to my installation, both in the design of the sink drains, and the path of the drain hose to the stem on the drain pipe:

Picture of similar sink/drain configuration

  • Bring the drain line through the cabinet as high as you can drill a hole then when sink drain gets water in it it won’t back flow into dishwasher – Kris May 18 '18 at 23:32
  • the gutters at your house should not drain into the sewer .... they should drain into the storm drain system or onto the street .... maybe you have the downspouts incorrectly connected – jsotola May 19 '18 at 1:00
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This sounds like a drain hose problem. If you can post a picture of the drain hose from where it leaves the dishwasher until it goes into the drain pipes (usually either into the pipes under the sink or into a disposal under the sink), that would be very helpful.

Key likely items:

1 - If the drain hose goes into the drain pipes past the trap then that would likely violate code and would definitely explain the problem. The trap is there to prevent sewer gases from getting back into the house - or into the dishwasher. If that's the case, you need to either move the drain hose so it connects before the trap or add another trap (and then connect it before the trap).

2 - Dishwashers require an air gap. There are two forms.

The first ("traditional" in my mind) is a gadget on top of a corner of the sink. The drain hose goes up to this gadget and the water has to literally go through the air (an inch or so) to then flow back down into another drain hose into the pipes. I highly doubt you have this because any sewer gas would be coming out of the air gap either all the time or every time you run the dishwasher.

The second method is a high hose loop. The flexible hose from the dishwasher loops up so that the middle of the hose is right up underneath the counter before looping back down to go into the pipes or disposal. The key is that water can't back up from the pipes through the drain hose into the dishwasher unless water was backed up in the sink just as high - which would be quite unusual (and quite obvious at the time). There is effectively an air gap inside the hose.

If you have a hose loop that no longer loops - i.e., the hose either was never installed properly or has fallen down - so that the highest point on the hose is not much above where it connects to the pipes/disposal then you will have problems. If you have this problem, moving the hose may be all that you need to do - just use a loop of wire or something to hold the hose up in the right place. If your hose is not long enough - or if you are concerned that it is filled with dirt, etc. - you can replace it for ~ $10 (US).


Update based on picture. There appears to be a normal trap (good). But the drain hose does not have a traditional air gap and only goes a couple of inches above the pipes. The highest point is significantly below the bottom of the sink, so it will definitely not function correctly the way it is currently installed.

It is hard to tell whether a longer hose with a proper high loop will be enough to solve the problem, but you should install a longer hose with a proper high loop anyway in order to have a proper installation. If the problem still happens after that then some more troubleshooting will be needed.

  • This is practically the same setup as mine: hicro.club/wp-content/uploads/2017/11/… – ajeh May 18 '18 at 20:38
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    @ajeh Assuming that's an accurate representation: 1 - trap looks fine. 2 - no traditional air gap. 3 - hose does not go very high, definitely not as high as it should, so it would be relatively easy for backflow to happen - which may be worse after a rain if storm drain and sanitary sewers are connected. – manassehkatz May 18 '18 at 20:45
  • I'll try to lift up the hose if I have slack. The storm drain and sanitary are separate in this subdivision. I have a storm pond within a 100 yard distance, and storm water goes there. – ajeh May 18 '18 at 21:02
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    Priceless! I pulled the slack of hose from behind the machine and lifted it to about the bottom of the sink - that's as much as I could, by about 4". We had a rain overnight, and now that I ran a cycle - no stench. You have saved me a ton of trouble, which is much appreciated. – ajeh May 19 '18 at 21:50
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According to this page you may be experiencing backdraftng. Pressure imbalance between inside and outside can be at its worst during a rain event.

That may be strong enough to draw sewer gas past the p trap.

Negative air pressure inside your home is the culprit behind backdrafting and accelerated by wet weather events. Thus, it is important to identify any possible risks within your home that could be causing negative air pressure. Common factors that result in negative air pressure with in your home include:

Bathroom and Kitchen Exhaust Fans Fireplaces Exhaust Ventilation Systems Tight Building Construction

Typically, plumbing vents and exhaust systems will be improperly installed too closely to a door, soffit vent, window, or bathroom/kitchen vent. Making sure your ventilation and exhaust systems are free of debris and installed properly is critical in eliminating negative air pressure in your home. Especially when the reentry of sewer gases is significantly worse during rain, sewer, or storm drain flooding. 

In addition the drain line in your cabinet should be routed through the cabinet as high up as you can get a hole drilled. That will insure that waste water from sink will not be able to back flow into the dishwasher drain line thanks to the “high loop”. enter image description here Lastly be sure to check this page for tips that help keep dishwasher smelling fresh

  • Would I not feel stench from the sink drains then? Why only from the dishwasher, and only if I use drying cycle? – ajeh May 19 '18 at 0:16
  • open the window during rain. that will eliminate any pressure difference – jsotola May 19 '18 at 0:58

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