Very well thought out. and executed.
I am very interested in getting some runner ducks myself.... I had Moscovys by accident when I was a Tweenager... Someone gave me five ducklings brought them home and said Ma Look what I got.... That was 40ish years ago....
I remember having them grow up and my moms complaints about the POO. on the patio and water skiing in it.
Any hoo Have you seen Metzer farms duck pens? They have plastic grates that sits over water that is constantly flushed and filtered. Something like that could be covered with pea gravel for esthetics Or may be a little larger gravel if Pea clogs the grates. Then the water under the grates could be pumped to the orchards. They have video of their pens on their site.
I know Its probably something way too expensive and impractical for home keeping .