The disposal is not a flow thru and some water ejected from the DW, will remain in the disposal, so, after a DW cycle, try vacating the disposal.

I'm not sure exactly what disposal you're referring to. I haven't got an under-sink garbage disposal.

It's less then common not to have a disposal.

However in your configuration the DW drain attaches above the trap, IE> between the sink and the trap.

So, instead of having freshly run water in the trap, you have waste water from the DW in the trap.

So, after a DW cycle, run some fresh water in the sink to flush the DW waste water out of the trap.

We don't have a disposal because we've got a septic system and don't want to add more waste than is necessary.

My husband suspected that the problem might be just what you're saying, snoonyb. Was it plumbed incorrectly? Should the dishwasher connection have been attached below the trap? I'll upload a photo.

Just another thought -- I run the dishwasher only 3-4 times a week, but I run water in that sink all the time. Still, the odor remains. Other than running fresh water, is there something else I can do to purge the wastewater from the dishwasher from the trap?

For those with more plumbing savvy than me:

Could it be that with no horizontal section after the trap but before the vertical drop, that running water from the sink syphons the trap dry?

Snidely, that is what I am thinking? Given that you continuously run water to the sink it is seeing relatively "fresh" water. I do not think the sink is vented correctly and the trap is being siphoned and you are getting "eau de septic" . Call the guy who did the plumbing.

The simplest solution would be one of Oatey's Suti-vents. I don't really like using them but while we were working into our re-model I had to eliminate the vent on the old kitchen sink. I installed one of these and it solved the problem.

Ahhh, an AV vent, good advice.

Were it I, given the loop of the DW drain line I would change it to the recommended high-loop which will create a natural airgap, instead of the present natural vent into the sink.

Some DW mfg. also offer the alternative discharge configurations in their installation instructions.

What, exactly, is a "Suti-vent" And what is an "AV vent"?

You can find them on plumbing suppliers web sites, you plumber should have informed you of this alternative, however, he may not have enough knowledge or experience, given the fact that he did not high-loop the DW drain.

They are used where there is a peninsula or island bar sink and in that configuration mount higher than the trap, in the cabinet, not obstructed from free air flow.

In your configuration, after the trap where the drain 90's thru the floor, you replace the 90 with either a santee or vent "T". Out of the top you pipe up higher than the trap and out thru the wall to fresh air.

An AV vent is basically a check valve that allows air to enter when water is draining then closes once the vacuum is released to prevent sewer gasses from escaping..

Took a while to find a photo . But here you go to show how one is installed on a double bowl sink. The AV vent is the black "cap" at the top of the vent pipe circled in red.

What the OP has is termed an "S-trap" and they are prohibited by the plumbing code pretty much everywhere that has a plumbing code. The reason being that the water exiting the bottom of the trap can siphon the water out of the trap, allowing sewer gas to enter the building. That could be the cause of the "musty" smell, and the fact the odor goes away after water has been run supports this conjecture.

The smell could also be caused by water sitting in the drain line from the DW. The drain line from the DW should atleast have a high loop reaching up out of the image shown, and then looping over and coming down to the drain attachment above the trap.

Or it could be that the greater water flow from the dishwasher drain causes the trap to be siphoned, whereas simply running a little from the faucet does not. (which in my opinion is the more likely answer)

Do not attach the DW drain below the trap. That will ensure that sewer gas can enter through the DW drain line.

There may be a way to remedy the situation with an AAV (Air Admittance Valve) depending on whether they are allowed by local code, but since they ought to be installed on the horizontal section after the trap you'll still likely need to reconfigure this to allow one to be installed.

I'd ask what the inspectors said at the end of the remodel project, but it seems clear there weren't any.

Lastly, the AAV that hippy shows appears to the the cheap spring-actuated kind that is prohibited from use anywhere inside a house. (I think they are only "legal" in RV's and mobile homes where the laws are extremely lax.)

Note: I don't claim to be a professional plumber, or claim to know all rules and exceptions of the plumbing code, but I've read enough here and on other plumbing forums to know that the person who did that plumbing shouldn't make any claim to be a professional plumber either.

This post was edited by bob_cville on Tue, Jul 22, 14 at 13:23

I will second the idea that the drain hose from the DW needs to be routed (and attached) up high in the cabinet, to the top of the sink.

Imagine if that trap gets plugged. Where will the water from the sink go? Right into your DW and out onto your floor.

"weedmeister "

"Imagine if that trap gets plugged. Where will the water from the sink go? Right into your DW and out onto your floor."

This is true for some of the older models, however, many of the newer have backflow preventers on both the supply and discharge lines.

msbrandywinevalley,

I saw that you received similar advice to mine above on a different forum. I love that other forum for plumbing advice, since it is frequented by many plumbing professionals. If you get a chance, stop back here and update us with how it turns out.