Duck Tractor

Recently I got a bathtube freebie on craigslist. Ive been wanting to redesign the duck tractor for a long time. to make them happy. I guess I'm looking at a sign that would allow for some water cleaning using duckweed or azolla or both. it's what i currently use to grow duckweed and azolla is water down duck manure. in shallow pools has got to be a way to integrate that with the tractor or possibly a tractor follow on?

I guess I'm looking for a bit of an out of the box design to test out. instead of the standard. I tractor muscovy ducks. they have a pole they can perch which they sometimes do. id like to scale back on chickens and bring the ducks i already have forward. taken over some of the jobs the chicken was doing. I just need to know the limitations. and understand better. or if it would be worth it to mix the ducks and chickens?