Dishwasher Odor Mystery

[nj385]

There is a problem with your vent on the discharge, and you are getting sewer gas back in. Not sure how. But that is my first guess. And, when you put the new unit in you didn’t change the discharge, which perpetuated the problem.

Now that this new information is known, I'd focus my attention towards your p trap, or lack thereof

I will try changing the discharge drain tube on the disposal and even lower the P-trap as to create a deeper water level to stop the sewer gas.

Actually, your p trap seems fine provided you have an accumulation of water inside of it to block off the sewer gasses

How much is known about your plumbing? Is there a window at the kitchen sink? Is it possible you have a faulty AAV instead of a vent that protrudes through your roof? All these could cause a sewer gas smell.

Your right about the P-trap, it is doing it's job and extending it would put stress on the garbage disposal trying to flush the waste away. There is a window above the sink and a stack vent on the roof off to the side of the window. No AAV unit.

 

[havasu]

I'm just guessing now (and the experts are probably sitting back laughing) but I would separate the discharge hose from the disposal and take a whiff to find out if the smell was coming from the dishwasher or the disposal. There has to be a solution to your issue.

 

[FishScreener]

Does the line from the dishwasher have an air break. I‘ve had problems with the disposal pushing back into the dishwasher enough times, that I generally want to install one of the air-break assemblies on the sink deck.

I know that destroys the sleek commercial countertop look some folks demand. But, If possible it is best to have one. Forty years ago I had to install one on a house where the owner had installed both the dishwasher, and disposal themselves. No air-break, and the disposal discharged into one of the split tees with the straight vertical separator in it. The back pressure that caused in the drain line was pushing waste back out the line from the disposal to the dishwasher.

If they ran the disposal, before starting teh dishwasher, no problem. If they ran the disposal with out running the dishwasher afterwards, they would get strange smells.

EDIT TO ADD: Filling the disposal, and then running it with more than a faucets flow of water through it, makes the problem of pushing things back to the dishwasher worse. If you do that there is more than the drain line can handle, (particularly if you have a sink full of water behind it), and the dishwasher port gets pressurized. Think of the disposal as an inefficient centrifugal pump. If you follow the directions and feed waste into it while running, with the faucet on. there isn’t a lot of pressure Generated on teh drain line. Run it like most folks do, with the waste stuffed in, it has more ability to generate pressure. Do it like my sister, who puts the waste in before she washes the dishes, then runs it as she drains the pan full of rinse water, and it will generate about a foot of head.

 

[Geofd]

Snake or camera you vent to rule that out

 

[nj385]

I'm just guessing now (and the experts are probably sitting back laughing) but I would separate the discharge hose from the disposal and take a whiff to find out if the smell was coming from the dishwasher or the disposal. There has to be a solution to your issue.

I just tried your idea and no significant odor. A couple hours ago we ran the dishes and again the odor is pungent. I'm really leaning toward a problem with the main waste line. Some kind of back pressure.

 

[nj385]

Does the line from the dishwasher have an air break. I‘ve had problems with the disposal pushing back into the dishwasher enough times, that I generally want to install one of the air-break assemblies on the sink deck.

I know that destroys the sleek commercial countertop look some folks demand. But, If possible it is best to have one. Forty years ago I had to install one on a house where the owner had installed both the dishwasher, and disposal themselves. No air-break, and the disposal discharged into one of the split tees with the straight vertical separator in it. The back pressure that caused in the drain line was pushing waste back out the line from the disposal to the dishwasher.

If they ran the disposal, before starting teh dishwasher, no problem. If they ran the disposal with out running the dishwasher afterwards, they would get strange smells.

EDIT TO ADD: Filling the disposal, and then running it with more than a faucets flow of water through it, makes the problem of pushing things back to the dishwasher worse. If you do that there is more than the drain line can handle, (particularly if you have a sink full of water behind it), and the dishwasher port gets pressurized. Think of the disposal as an inefficient centrifugal pump. If you follow the directions and feed waste into it while running, with the faucet on. there isn’t a lot of pressure Generated on teh drain line. Run it like most folks do, with the waste stuffed in, it has more ability to generate pressure. Do it like my sister, who puts the waste in before she washes the dishes, then runs it as she drains the pan full of rinse water, and it will generate about a foot of head.

I do not have a Air Gap installed. I was thinking of trying one. Who knows, it might work. Thanks.

 

[nj385]

I just tried your idea and no significant odor. A couple hours ago we ran the dishes and again the odor is pungent. I'm really leaning toward a problem with the main waste line. Some kind of back pressure.

I'm going to try a Air Gap. It just might work. Thank you for your time effort to figure this out.

 

[havasu]

Good idea. Do you have room to install one?

 

[nj385]

Good idea. Do you have room to install one?

Yes. I will replace the soap dispenser and install it there. I'll let you know what happens in a few days. Thanks again.

 

[nj385]

I installed the air gap yesterday and ran a load of dishes. The odor has decreased substantially after the first wash. I hope it remains this way after a couple more. Thank you for all your help and hopefully you will not hear from again.

 

[Geofd]

That's good hopefully it goes away completely!!!!!!!

 

[havasu]

Please let us know after a week or so. I'd just like to confirm this was the exact fix.

 

[nj385]

2nd wash and no odor. It looks like the air gap worked. I still would like to know why the back wash happened. I guess it will remain a mystery. Thank you for all your help.

 

[Twowaxhack]

We use the high loop method here and no problem for the past 90 years.

We’ve never installed a residential air gap .

The problem we get is people with garbage disposals and the dishwasher hose drains through the disposal. This will cause the disposal to stink because the dishwasher water drains into the grind chamber and the garbage disposal can filter out pieces food. This sits in the disposal to rot if it’s not turned on and rinsed out.

I’ve only found one or two countertop air gaps in 35+ years in a service area of 500,000 people.

To each there own but I’ll never use those countertop air gaps. They flood kitchens.

 

[FishScreener]

We use the high loop method here and no problem for the past 90 years.

We’ve never installed a residential air gap .

The problem we get is people with garbage disposals and the dishwasher hose drains through the disposal. This will cause the disposal to stink because the dishwasher water drains into the grind chamber and the garbage disposal can filter out pieces food. This sits in the disposal to rot if it’s not turned on and rinsed out.

I’ve only found one or two countertop air gaps in 35+ years in a service area of 500,000 people.

To each there own but I’ll never use those countertop air gaps. They flood kitchens.

That is why you install them in the sink deck. Which usually has a rim outside of the hole to capture the water.

And, the high loop doesn’t always work with high horsepower dishwashers. Particularly if the drain lines aren’t set up correctly. If a tee with the diverter plate, in the middle is used, it chokes the discharge from the grinder and it will back up through the dishwasher line if it is connected to the grinder. Comes from using the inexpensive kits to plumb the waste lines. The cheap ones have a tee with a diverter plate to push the water down, and keep it from coming up the drain into the other sink. That issue is better solved with a real sanitary piece that has actual radiused legs, which eliminates the waste shooting straight through the tee to the other drain.

Unfortunately most of the big boxes and hardware stores, the homeowner shops at, only have the cheap kits available. So, that is what folks install when they install a new grinder. My current house, the previous owner, had installed a wye where the line comes out of the wall, and each basin has it’s own line to the wye. it is an effective setup, but eats a lot of the space in the cabinet.

 

[Twowaxhack]

That is why you install them in the sink deck. Which usually has a rim outside of the hole to capture the water.

And, the high loop doesn’t always work with high horsepower dishwashers. Particularly if the drain lines aren’t set up correctly. If a tee with the diverter plate, in the middle is used, it chokes the discharge from the grinder and it will back up through the dishwasher line if it is connected to the grinder. Comes from using the inexpensive kits to plumb the waste lines. The cheap ones have a tee with a diverter plate to push the water down, and keep it from coming up the drain into the other sink. That issue is better solved with a real sanitary piece that has actual radiused legs, which eliminates the waste shooting straight through the tee to the other drain.

Unfortunately most of the big boxes and hardware stores, the homeowner shops at, only have the cheap kits available. So, that is what folks install when they install a new grinder. My current house, the previous owner, had installed a wye where the line comes out of the wall, and each basin has it’s own line to the wye. it is an effective setup, but eats a lot of the space in the cabinet.

Yeah, we don’t experience your issues here for some reason.

Our sink decks don’t have rims. When is the last time you worked in a modern kitchen ?

Post pics of the sinks or countertops with an air gap that won’t flood the kitchen, I’d love to see what you think everyone should have.

If the disposal is pushing water up through a high loop, the drain is partially clogged. It’s that simple.

Modern dishwashers have check valves before the discharge hose connects to the unit so even without a high loop most don’t backflow unless the valve is inoperable.

This isn’t a new debate. If high loops were a problem with 500,0000 homes in our service area we would’ve already had problems.

But everyone can do as they see fit but I’ll never install an air gap on a residential and if I do it won’t be there very long, just long enough for the inspector to leave.

They’re trash…..

 

[Twowaxhack]

So the original poster is starting his dishwasher then comes back a couple hours later after the dishwasher has washed, rinsed , dried the dishes AND then makes his disposal shoot water back through the high loop ( some how ) AND…..Then opens the dishwasher and smell stink from the disposal water.

I just don’t believe that’s happening, call me crazy.

Garbage disposals have been known to stink. Dishwashers have been known to stink.

I suggest making sure the dishwasher drain hose isn’t wadded up under the dishwasher to where it’s making it’s own ptrap of stinking water.

The hose should rise continuously until it reaches the high loop and then back down to the drain.

But even so, there will always be some water left in the bottom of a dishwasher, it doesn’t pump out drain.

 

[nj385]

We use the high loop method here and no problem for the past 90 years.

We’ve never installed a residential air gap .

The problem we get is people with garbage disposals and the dishwasher hose drains through the disposal. This will cause the disposal to stink because the dishwasher water drains into the grind chamber and the garbage disposal can filter out pieces food. This sits in the disposal to rot if it’s not turned on and rinsed out.

I’ve only found one or two countertop air gaps in 35+ years in a service area of 500,000 people.

To each there own but I’ll never use those countertop air gaps. They flood kitchens.

I too have never installed an air gap and always a high loop but for some reason the high loop did not prevent the backwash. I even removed the garbage disposal and did a straight connection and no change. A mystery.

 

[havasu]

I too have never installed an air gap and always a high loop but for some reason the high loop did not prevent the backwash. I even removed the garbage disposal and did a straight connection and no change. A mystery.

That's for sure!

 

[Twowaxhack]

Maybe the check valve that’s integral to the dishwasher isn’t closing or isn’t present.

Disconnect the drain hose and connect a clean hose to it so you can blow through. ( don’t be putting your on a dirty hose) Try to blow backwards into the dishwasher from the drain hose.

You shouldn’t be able to……