Is there any species that flies but lands specifically to poop? That seems very inefficient. Though I guess dragons couldn't really glide like birds so they wouldn't save that much energy by staying airborne.

I assume they have cloacas right?

I don't kbow about reptiles but birds are dinosaurs and I have a pigeon that escaped from a for meat breeder and when I took her to a bird vet they said pigeons don't actually poop while flying and they usually have some microbe or something that gives them diarrhea. After getting her treatments she poops out solid nugs.

So I would say ground or high perching point unless they have some sort of health condition.

Birds are dinosaurs, not reptiles. So, the pictured T. rex (a dinosaur) is a bird and does thus not count for "reptiles that do air".

I think they are Imodium gang

I'd think so, but that doesn't resolve the question.

Birds are reptiles too, and many of them are ground poopers or even water poopers!

Have you considered they could be water poopers? Like ducks?

They're ATP, All-Terrain-Poopers