I should also add that I called Miele, and after being on hold for 20 minutes, was advised to “contact an electrician”. When I explained that my question was misunderstood because it was a plumbing issue, I was put on hold again and then the call cut out.

Following. Want to do the same.

You can use a Dual Air Gap with the two hoses that came with the dishwashers plus a third, 7/8" ID hose (example) between the air gap and the garbage disposal's dishwasher side drain port

Yes, I do not want to tempt fate by running both machines at the same time - but I do dream of not needing to put dishes away to turn around and load them back in 2-3 times a day. I’d just like a clean dishwasher and a dirty one so that my children can never again feign innocence and ignorance on if the dishwasher was full of clean dishes and therefore could not possibly accept their dirty ones 🤣

I appreciate the idea. I also don't know your location's code compliance rigidity. Just because you can ameliorate waste flow interactions by alternating operation doesn't mean some future person won't run them simultaneously. The risk here is certainly less hazardous then certain fire causing practices that the National Electrical Code was established to avoid. Plumbing codes are generally driven by sanitation considerations.

Putting in a trap and standpipe into an existing configuration may be difficult when the dishwasher drains to a connection in the wall, at least without opening the wall. There may be options for going down through the cabinet and floor past the standpipe trap. I think you should consult with a plumber who should know how to conform to code and still accomplish a somewhat unusual hookup configuration.

@kaseki I’m not worried about code and am not selling ever unless I win the lottery (and it better have 2 dishwashers). If I were to ever sell, I would disconnect one and let the new owners decide.

The Miele machines have anti backflow pumps and don’t need air gaps. Lines would be joined only with high loops. But a suitable connecting piece escapes me, but it IS made for dishwasher drawer configuration. Any ideas on a coupler?

"The Miele machines have anti backflow pumps and don’t need air gaps."

Whether air gaps are needed or not (and they're supported; see page 75 of the operating instructions) the dual air gap above solves the problem, allowing both dishwasher to be connected to the garbage disposal. Why not use that?

Doesn’t that require an air gap on the counter top? Or can it be jimmyrigged just underneath?

The air gap sticks up through the countertop.

I don’t want to cut out my countertop and look at an air gap forever, thus my hunt for a Y connector that would be functional with a high loop and not running the machines simultaneously. They make this gizmo specifically for the drawer machines (Fisher Paykel), so it has to be functional, but those drawers have smaller than standard outlet tubes.

https://applianceparts365.com/fisher-paykel-joiner-drain-hose-dbl-us-part-529872?gclid=CjwKCAjw0a-SBhBkEiwApljU0o0Qvxlv5MSszXb_yuo8ZXNgUpLl90Zr9INI8GYKSmDJBS3x_PByGBoCXI8QAvD_BwE

https://www.searspartsdirect.com/product/1f755ea3qs-0011-665/id-WPY6919906?sid=pla:ggl:WPY6919906:pla-294682000766&gclid=CjwKCAjw0a-SBhBkEiwApljU0pvjkeUBsEFhPyisprs9aSnKD1XwqClUl9muS_nAuahzZ3-TJYadKBoCu8QQAvD_BwE

The Y-connector above is also on Amazon: https://www.amazon.com/dp/B09CTJ8VCF

You'd just have to make sure the drain hoses from the dishwashers would fit onto this connector and that you had some way to secure the hoses to the connector. If I remember correctly, my Insinkerator garbage disposal came with a clamp for the drain hose.

I do not know of a particular suitable coupler because I have never needed one, and don't use the garbage disposal as a dishwasher drain. Standpipe solutions intrinsically provide an air gap.

Mieles have an oem drain hose with a valve at the hookup point when connecting to a disposal. If you can fit both discharge hoses with their valves to one of the above y pipes, I think it'll work.

Use the linked part please.

The linked part is 5/8” and a Miele drain hose is 7/8”. I was sent this photo as a solution, so I’m going to get this vertical piece and use a high loop on the lower hose unless someone has a reason why it should not be done?

Page 75 of the operating instructions notes case where air gap must be used.

>>>"I was sent this photo as a solution,..<<<

For the benefit of later readers, can you say who sent the photo? Miele?

There should be a high loop on both drain hoses, although more tricky to configure on the higher disposer connection. I know someone who doesn't have a high loop on their drain hose at a disposer connection. Their dishwasher flooded the kitchen twice. The most recent instance was due to a clog of grease in the drain hose presumably from disposer backflow along with the dishwasher overflow float being stuck so it overfilled. Their dishwasher is a Frigidaire which has a backflow flapper on the drain pump but that doesn't prevent backflow downhill from the disposer into the drain hose.

@jwvideo That photo is from someone local with a $300k kitchen remodel, so I’m hoping their contractor’s subs did things properly and not just expensively. 🤔

@dadoes point taken!

You should be looking at connecting up high to the branch tailpiece, not the garbage disposal. Going in the top inlet of the disposal is very noisy when draining, and if the other single branch tailpiece DW connection is too low it may get backwater. Here are a couple to look at, make sure to read the reviews for definite issues and I do not know about code compliance for this situation.

Dual Hose tailpiece

Dual hose adapter

Thank you

Do you have a final update for us?! I would LOOOOOOOOOOVE to know the ending!!!! I'm in the same boat. 5 young kiddos who have never finished a full drink from one cup before getting a new cup. I'm dedicated to having two dishwashers. Hope things went well!

Yes! The solution was so easy, I truly can’t believe how difficult it was to come up with…
One dishwasher is connected directly to the punch out in the garbage disposal. The other dishwasher is connected to a simple drain pipe tap in - the type you would use if you did not have a garbage disposal installed but did have a dishwasher. I bought the tap in piece at ACE Hardware - easy peasy - and installed it myself. It has all worked flawlessly for ages now. My neighbor with the nearly $300k kitchen has hers installed the same way and it’s been doing just fine for over 2 years now. If you dream of two dishwashers, I highly recommend it. And if you can install your “main” one directly across from drawers where your usual bowls/dishes/utensils live, you will revolutionize the efficiency of your life. I get a jolt of joy every time I stand in one spot and unload 90% of the dishwasher without taking a single step!

Gee - I'd think you'd get more than 2 dishwashers for $300k! heehee

Glad you found a solution.

Ha - yes -because 2 is the perfect number even when you’re building the kitchen to inspire all kitchens!

Picking up on this as I want to do thethank same thing - did you have to use the countertop airgap?

@Cynthia - I am in Los Angeles so ymmv with code, but she and I both have Miele dishwashers (highly highly recommend! - far superior to the Bosch at my prior house) which use pumps to clear the drain lines. They do not require air gap installation or high loop drain line positioning. I have only a garbage disposal countertop air button, the faucet hole, and a built in soap dispenser (with the kit that screws into the giant jug of soap under the counter) on the counter.

Thank you! Great info!