Have you cleaned the filters? Another idea would be dirty backflow due to an air gap problem, though less likely.

Definitely look at cleaning filter first. Then take a look at your drain hose - many times they are a semi-opaque plastic. If it looks like it’s full of nasty stuff that may be your problem. I had a rental once with this issue. I tried everything and we finally had to replace the drain hose, it was FULL of nasty dark moldy gunk.

Yes, clean the filter. I use Oh Yuk! dishwasher cleaner specially made to get rid of buildup, I use it maybe 1-2x/year so a bottle lasts me a while. Dishwasher Cleaner – Oh Yuk

- It could be dirty filter - very easy to clean - what is your dishwasher model?

- It could be what @catspa mentioned above about dirty backflow, which is actually quite common. The cure is very easy - it's called a "high loop" hose. If your dishwasher is newer, it should have come with the high loop hose installed. If your dishwasher is older, whoever installed it might have omitted the high loop hose. Here is a diagram to show the high loop hose, so you can see how gravity would work to prevent dirty dishwater from backflowing back to dishwasher. Here is a link to a video explaining the high loop and how super easy it is to install it.

Here's pics of under my sink.

Not sure if this is the high loop you're referring to, or what that could be.

I have a Bosch dishwasher, to the right side.

I also don't have an air gap thingy on the counter.

BTW, the dishwasher filter is sparkling clean, so that can't be the issue.

No high loop in sight there and even looks like the drain line has some gunk settled in that bend.

Yes, clean the filter. I use Oh Yuk! dishwasher cleaner specially made to get rid of buildup, I use it maybe 1-2x/year so a bottle lasts me a while.

No, cleaning the filter doesn't mean running a load with a special product. It means removing the filter and cleaning it. You're supposed to do it about once a month.

Check You Tube for a demo of how to do it.

No high loop in sight there and even looks like the drain line has some gunk settled in that bend.

The tubing is about 1 inch away from the countertop. Would lifting the tube 1 inch higher make much difference? The end connecting to the dishwasher falls dow to the floor (beyond the wooden partition).

Or, is there something else I should do besides lifting the tubing 1 inch?

@Mary Weber, Do you mean 1 inch away from the bottom of the sink? (which is what I see in the photo, not 1 inch from the countertop) There doesn't seem to be much of an arc above where the drain attaches to the garbage disposal -- in fact it slumps downward from where its attached to the disposal before going up a bit to get over that partition. So there's a lot of height to the highest part of the drain from the dishwasher side but not much at all from the disposal to that highpoint, where the drain sits on that partition, which seems like it might allow siphoning from the disposal, back into the dishwasher. (I frequently set up siphons to drain fish ponds and such in my backyard and as long as you have enough downhill slope where the drain hose ends, you can pull water up over some pretty good slopes along the way and the siphon will still work.)

If you look at the video @M Miller posted, the guy talks about attaching the top of the loop way higher, up BEHIND the sink, which would give it much more of an upward arc from the disposal and better to prevent siphoning from happening.

This is the high loop coming into the cabinet on my Bosch. I think this was pre-set on the back of the DW on mine.

I've never seen flex hose used as a sink drain. I am surprised you have nasty odors in the DW but not the sink.

Whether it's the cause of the smell or not, I would definitely install a proper plumbing drain.