I’m getting ready to install one of these so I’m personally invested in this conversation.

Does it flush differently than your other toilet? Is it a dual flush or single flush model?

No clue. Only will say that IF your renovation included a move of the loo from a different locale, that soil pipes are a "perfect pitch" issue. Not too much, and not too little. It may be "clear" as the plumber stated, but perhaps............? The back flow is pitch.

https://www.archtoolbox.com/materials-systems/plumbing/pipe-slope.html

It's a dual flush, new install, new plumbing as we added a wing to our house, and this is in new ensuite. The other install I was referring to was in another house, still working perfectly.
The 'pitch' comment is interesting... Guess that means removing the toilet from wall, taking out drywall to reveal the wall mount and piping.

Wellllll it all goes somewhere after that wall mount. Who knows? Could be the Gerbit carrier and an elbow, the vent, the size of the soil pipe.....it is WAY beyond my pay grade, that much is certain. We need Joe......: ) Good luck!

Is the drain in the slab or crawl space or?

Something is not installed properly and we have no idea what went wrong but IMO the plumber did something wrong . Was there a toilet in that spot before , is this new build you need to provide more info even for Joe.

"It's a dual flush, new install, new plumbing as we added a wing to our house, and this is in new ensuite. The other install I was referring to was in another house, still working perfectly."

It's a new install, 2nd floor, with new stack and vent. Tested venting on a cold day, steam from exterior. Plumber said he scoped, found small amount of drywall debris, which they are saying is reasonable. .... Goes to new floor connection and tied to existing main under basement concrete floor. Floor is finished with platon membrane and LVT. There is a clean out on the bottom of stack, so I can have my plumber open that and check.

Will contact Duravit, thanks for reaching out.
And will let the rest of you know how this turns out.
FYI the contractor is suggesting changing toilet out for another model, same carrier.

maybe change out the plumber? !

Final word from plumber - basically this is as good as it gets. Flush 2 or 3 times at max to clear solids. They changed out to Durastyle, same carrier. Plumber says we will get used to it....

Would not recommend the Duravit.
The ten year old model I had installed at previous property uses more water per flush, older model obviously. This new, 1.6 litre per flush model does not work. Even dye test, the water is not clear on a single, max flush.
Looks great, easy to clean under but the mfg will have to go back to the drawing board. Contractor says I'm stuck with it. Changing manufacturer and I have to pay for full install, changing carrier, etc.

Can you tell me which model duravit this is as I'm about to install a duravit wall hung toilet with the gerberit carrier? I'm getting a little nervous about this, anyone have suggestions for wall hung toilet for gerberit carrier that are not very expensive? Thank You

The Duravit model originally installed was Darling 25450090092
Replaced with Durastyle 2220009. Both use same Gerbitt carrier, slightly different look, different wall 'print'. Drywall repair necessary.
The issue, as plumber explained is the interior chamber which waste flushes to. It is trap, up from the bottom of bowl, and there isn't sufficient water to push waste past this point.

I gather that in the redesign to reduce water consumption the mechanics are not functioning as they should, at least not with the water pressure and volume that we have in Canada.

As I said before, my 10 year old model functions perfectly.

Thank you, I'm installing the starck 3 I hope I don't run into these issues.

Tip..............flush as you GO. ( No, I am not kidding ) Then one last flush with the tp. . Sorry, but anything less on toilets these days is asking for trouble. I mean ALL of them. You can thank the government.

They can't stop you from taking thirty minute showers. They can make you HATE any toilet.

God Bless the Donald. He's not messing with your light bulbs. Want the incandescent? It's your business. Have them. Turn them off when you get done with that second, flush, and don't firget to wash your hands. That's from "mom"

Did you reach out to our technical support team? It might be an installation issue of the in-wall tank and carrier causing the toilet bowl not to evacuate or a line restriction. Please feel free to reach out to us for additional support. Mo-Fr 8.00 - 5.00 > Ph. 770-931-3575

The good news is the replacement Duravit Starck 3 works MUCH better than the original model. And yes, the builder reached out to local Duravit rep in Montreal, Quebec, Canada. I was not involved in the discussions.