Great Site!

[TammyLB]

Hi and thanks for this great site!

I need to ask a question. My Mom has a built in dishawasher and garbage disposal, there is a sewer smell coming from the dishwasher. They have had smoke tests done, everyrhing came out ok on that. They went and bought a new dishwasher, had it installed and the smell is still there. So I went and put all new pipes under the sink thought that might be it, it wasn't.

Where can we go from here?



Thanks so much for all your help!

[master plumber mark]

do you have a separate trap for the dishwasher???

or is it going over to the disposal....??

put a loop in the line if necessary to the disposal..


but you should not be getting any odor from a dishwasher
even if it is directly droppping into an open line..

is the smell more like a "rotten egg" type smell???

[Mikebarone]

There is a device that is called an “air gap device” that is mounted on the top of the sink, and this prevents the discharge water, (from the dishwasher) from going back into the dishwasher. If you don’t have an extra hole in your sink, (next to your faucet) you would have to drill a hole for it….so you don’t’ want to go that way.
Check under the sink, and see if the discharge hose has a loop in it, (like Mark was saying) and the top of that loop should be mounted (or braced) as high as you can get it, in the cabinet area under the sink. That will do almost the same thing as the, “air gap device”.
I have worked on a dishwasher that after it was completely done with its cycle, would hold water in the bottom of the washer. After reading the manual, (yes, I read the manual) it stated that it was normal to do that.
Now, this is far fetched, but something you might check. Under the sink, and after the U-shaped trap, make sure the drain line has positive fall away. I had a client that had the same exact problem and when I investigated it, I remove the trap, and almost fell over from the smell. As it turned out, it looked from the area out side of the wall that there was positive fall, but when I looked into the drain pipe, I could see that the pipe just inside of the wall turned a 90 degree, and then the pipe went up hill! So all of the bacteria was backing up, and would contaminate the trap water. If you dump some bleach water down the drain, and the smell goes away for a while, but then comes back, you might check that out.

Good luck,

Mike

[hj]

If the odor is not in the drain pipes, which is the usual cause, then it is probably the disposer itself. Very seldom the dishwasher.