Ah, the lowly "sink wart".
Back when DW started to be built-in, the dishcharge was connected to the sink or waste line,
When it was discovered that waste water from the sink was showing up in the DW,the "high loop" became a code requirement.The high loop was a configueration where the DW drain line is up to the underside of the rough top before connecting to the drain.
Then came the sir gap. Its purpose is to prevent backflow of waste water in the event of a power loss, and yes its a code required fixture.
However, with the use of a Miele DW many have successfully argued to excuse it, as there is one built into the appliance.

I don't know of any DW made today that needs an air gap. However, many municipalities have Codes on the books from years ago that are obsolete but were never removed. So, some people are forced to install an air gap even though they're no longer needed (parts of California, for example).

Yes, they are for the overflow from the DW. Do you need one anymore? No, just be sure you have a "high loop" installed (it should be if a plumber installs the DW, but if you're DIY be sure you do it).

What if you need one to meet code? Put it in b/c you will have to to pass inspection (unless you're up for a battle w/your Inspectors) and later replace it with a soap dispenser.

Thanks for all the info - originally my dishwasher drained into its own drain (not hooked up to the sink drain) - house was built in the 50s & this drain went through the basement, & out through the garage - it didn't even have its own shut off. Last week, the plumber took that pipe out & hooked it into the garbage disposal with its own seperate shut off under the sink. He said this configuration would improve performance of the dishwasher? The tubing out of the dishwasher goes up & behind the drawer of the base cabinet that is in between the dishwasher & the sink (Sorry - don't know if I am describing this correctly). Is that what is meant as a "high loop"? He has not mentioned anything about an air gap, so I'm guessing he's not planning on installing one? Guess I need to add that to my punch list to ask about tomorrow.

air gap - a device that befuddles some people who install it in such a way that it floods counters and warps cabinets. If you have to have one, make sure the plumber installs in such a way that it expels into the sink and not onto the counter.

I don't know enough about plumbing to be sure if the high loop thing takes care of backed up gunked up sinks... In places I've lived before (rental), the dishwasher water bubbling out through the air gap was a sign that serious snakeage was necessary. I think it's a great early warning device. :) (Though maybe unnecessary.)

What Plumeriavine is talking about is new installation (not old and gunky), which is a bad bad thing.

Just fyi, the air gap is unknown on the east coast -- it appears to be a Western thing. Many of us only know this elusive beast from fellow Gardenwebber's pictures; I've never seen one live.

From previous threads on the topic I gather that California and Nevada still include it in their code, but almost all other locales in the continental US are fine with the "high loop" solution.

I'm on the Right Coast, and pretty much whereever I've lived, theree's been an airgap device. First time I saw one I didn't know what it was. Until it got stopped up and dump dirty water over the sink.

Anyway, its there to make sure that a sink backup does not dump water or syphon into the DW.

Washington also includes it in their plumbing codes, but Oregon does not. Crazy. I just replaced mine with an air switch of the garbage disposal once the inspections were done.

I live in California and have had one in the old kitchen for 25 years. Never knew what it was until I discovered GW when planning the new kitchen :-) Thought it was just something to plug an extra hole.

Have to have one in the new kitchen. Everyone here has them. Also, I have NEVER had any water or anything come out of it. It's just there and to be honest, not a big deal.

But, of course, if I didn't HAVE to have one, I wouldn't!

Ditto to the first answer from snoonyb about looping the drain hose high before it comes down to the kitchen sink drain (or to the disposer).

When I called Miele daily for support, they never once said their DW had an integrated air gap. Also I've never seen it in any MIele documentation. ALso, no salesperson has ever mentioned it. In fact, this is the first time I've ever seen a mention like this.

In many forums for plumbers I've seen lively discussion about the need for air gaps in circumstances that will hardly ever happen.

It's a plumbing thing, for safety.
High loops cover almost all the same circumstances.
I don't think there ever was any DW that "needed" an air gap.
It was always for plumbing purposes.
Public health depends on your plumbing because you can't have your supply water getting cross-contaminated.
If plumbers are divided on this, then we may never know if air gaps could provide greater safety to the public water supply.

Do they let water gurgling noises out, when the DW drains?
I've practically never been in an airgap-equipped kitchen when the DW is draining, so I wouldn't know.
In this forum, it seems people aren't bothered by this.

hth
-d

There have been reports here of people using separate plumbing for their dishwashers to reduce drainage noise. Unless required by local code that an air gap be above the counter, the International Plumbing Code allows a standpipe under the counter, so long as it meets some minimum dimension between the weir (of the trap) and the top where the dishwasher drain hose connects. Note that the air gap is at the top where the hose hangs, just as it is for normal washing machine drain connections. Mine hasn't been tested yet, so I can't comment on noise.

kas

We are in WA so it's required. Once final inspection happens a high loop will be installed and the current air gap will turn into a soap dispenser.

We had an air gap before the reno - 6 years - and not once was there any water that came out of it.

When DH first hooked up the DW this time, he forgot to do something so when we ran it as a test, water came shooting out the air gap all over the counter as plumeria said. I just soped it up with a towel as the water came out.

So in essence, to me, the air gap is useless because it would end up flooding the window area, ruining the wood window casing, and likely seeping down and ruining the cabinets too. It's sitting as close as feasible to the sink right now. Apparently it needs to sit practically in the sink to drain fully INTO the sink.

It may be good to point out that an air gap provides a physical separation between the drain of the DW and the other drains (contaminated with dangerous bacteria), and that this separation (air space) helps in spotting blockages and helps to prevent contaminating your DW innards with rotten food from your kitchen drain. --- A high loop doesn't. --- For the record, an air gap serves a purpose, and some of this has already been described earlier in this thread, e.g. when pllog mentioned water visible on the counter.

I'm not installing an air gap. I'm installing an indirect drain (standpipe) that will have its opening at a level higher than the kitchen counter. I have wall cavity space available to make a recess for this.

All pumps need venting (access to air), in order to raise pumped water up in height. Washing machine drains need a standpipe, open to air, not taped shut to stop the gurgling. Basement toilet pumps need a lot of venting. This is one subject I've not seen discussed in GW appliance or kitchen forums. One way for a DW to compensate for a lack of venting is to pull new air from a vent on the side of the tub, or new water, and this small new volume may be sufficient for a small discharged volume (like DW discharge). Dishwashers with a high looped drain hose are "plumbed" like S traps just as many toilets are too, and must compensate for it by adding new water to keep the seal and to replace the volume discharged (many toilets do this too).

I did mention previously in this thread that Master Plumbers are not all in agreement about the "need" for air gaps (for dishwashers) so I hope that my remarks here do not inflame anyone. I hope to make it clear that air gaps are a code required plumbing device that can protect public health. In places where air gaps are not code, a slightly greater risk is run. It's not up to me to decide that "nobody needs" an air gap, and it's not up to me to tell the world that "because it's a Miele" one won't need an air gap. I've seen many posts from nice people who have purported that air gaps are not necessary, and also that one specific manufacturer is somehow exempt from this air gap question. Suspiciously like promotion and misinformation. It's not specific to any one machine or make. It's a plumbing question, and a DWV plumbing question at that. It's not up to kitchen-adddicted people to decide what public health questions they can rewrite to suit themselves. It certainly is not a desirable state of affairs if they go telling newcomers something simplified and inaccurate based on partial knowledge.

If we want, we can use this thread (or start another one) to invite new posts from Master Plumbers and experts in public health questions. There are documented cases of people dying because of cross contamination.

If anyone has anything to add, please add something new instead of parsing my words. I'm not a Master plumber.

hth