What's the width of the cabinet(s) between the dishwasher and the sink?

Is your drawing the actual configuration of the drain they installed? Presumably the wall is now closed up, right?

Can you post a couple pics? Leak area, area under sink, and wide shot of DW & sink in same pic.

I'll try to get some pics later. Yes the walls are closed up. But all of the dishwasher drain pipes are exposed because behind the dishwasher is a utility room on a lower floor (split-level house) and therefor accessible. Also where both the sink drainpipe and dishwasher drainpipe tie in to the main stack is also exposed fully in the utility room.

It is a U-shaped kitchen where the dishwasher is around the corner and a few cabinets down from the sink. Again, I'll try to get some pics.

Here are some pics.
The spot that spews water is the blurry pic where the flex hose enters the vertical pipe (kind of like how a washing machine drainpipe would look)

I was considering a very similar set up and I am really surprised to see the way that hose just goes into the drain. I know that codes are different everywhere so maybe this is a silly question but can't the drain hose connect to the drain under the sink or to the garbage disposal unit by snaking it behind the cabinets?

Takkone,
Judging by your pictures especially the first pic of the kitchen, it doesn't look like you have an Airgap installed??? Typically they are installed on the sink next to your fixture (Here in California where I live its code). Dishwashers will not drain properly without one. That should solve your problem, you may be able to get away with an Airgap installed at the drain pipe downstairs? Your contractor should know this?
Here's a link to a company that makes all different Airgap designs:

http://www.airgap.com/dishwasherAirgaps.htm

Let us know what works.....

I live in NY state and have never seen an air gap installed in anyone's kitchen, ever. I know in CA it is code but nobody installs them in NY. But any case I think the fact that the drain hose is not tight-sealed to the drain line constitutes an air gap. Kind of like how a clothes washing machine is often installed.

Good pics. Soon enough I would expect lazypup to chime in here with his professional advice and describe what's wrong with that configuration.

At the very least it looks it's pitched improperly, the connection to the vertical looks like a tee and not a wye, and we'll probably find out that the drain opening is lower than the rim of the sink.

Stay tuned.

Call back the contractor and have their PLUMBER come and look at it. Something seems wrong with that configuration and it probably doesn't meet code.

"Dishwashers will not drain properly without one."

They surely will.

Many places do not require them and are satisfied with a simple high loop.

There is no reason a drain line could not have been placed through (or even behind) the cabinets to get to the sink drain.

The standpipe acts as an airgap.

Q: where is this standpipe in relation to the DW? Directly behind or in the basement floor below?

What is the approximate horizontal distance from the trap of the standpipe to where it joins the vertical pipe?

What is that black section of pipe to the left of the standpipe, partially hidden by the copper pipe? Is that an Air Admittance Valve?

where is this standpipe in relation to the DW? Directly behind or in the basement floor below?
A: The standpipe is directly behind the dishwasher, the trap is about at floor level (the floor the dishwasher is on).

What is the approximate horizontal distance from the trap of the standpipe to where it joins the vertical pipe?
A: I would say about 4' - 5'.

What is that black section of pipe to the left of the standpipe, partially hidden by the copper pipe? Is that an Air Admittance Valve?
A: Yes.

No air gap is required, however the AAV is installed incorrectly.

The AAV is installed on the standpipe, but the standpipe is already open to atmosphere on top so no vent is needed.

The AAV should be installed on the drain line at least 2pipe diameters downstream from the trap weir.

I would begin by installing the AAV in the correct location and see if that resolves the problem.

If not, that appears to be a 2" drain line. You could increase the diameter of the standpipe to 3" to allow a bit more volume.

Some may argue that you cannot increase the size of the standpipe because you cannot decrease the size of a drain in the direction of flow, but that would not be correct. A standpipe is not a drain, it is a fixture and increasing the diameter of the standpipe would have the same connotation as installing a sink. In this case the actual drain opening is the inlet of the trap.

"however the AAV is installed incorrectly. "

Must have used the same plumber a place I used to work at did.

They had carefully installed an AAV on the wrong side of a water fountain trap on the manufacturing floor.

The building engineer was to dumb to even recognize the problem.

He could never keep our 400 Hz generator system (simulates aircraft power) working worth a darn either.

Let alone our 28 VDC system (almost 1,000 amps worth).

He just could not understand that the breakers he purchased and wanted to use would not work at 400 Hz, let alone at DC.

Solved - I had a plumber come out and snake the line. There was a clog of hair that was significantly slowing the flow. Once that was cleared, the sink can be filled to the top with water and it drains now without a problem. Thanks all.

LP is correct about the AAV. That's why I asked.

Also, since this is a DW, not a cloths washer, how high must the stand pipe be? Above the flood level of the sink?