Plants for a Reused Bathtub Duck Pond

I've repurposed an old bathtub as a duck pond. Are there any plants I can grow in the tub that would help with water filtration and also give the ducks some munchies?

I'm not sure you can have both, from what I understand ducks are voracious, and a bathtub is a small space.
Maybe use the duck spoiled water to irrigate terrestrial plants,or on plants that are out of their reach?
Duckweed and water hyacinth would probably be the best water plants.
Reeds might be more useful homesteading wise.
Willows are notorious for being consumers of waste water.
Cattails need some soil, I think,but produce a lot of useful stuff and food.

I have muscovies, and in my experience you will definitely need to protect any plants you want to grow around ducks. You can however fertigate with your duck water and it is fantastic as an all around nutrient source (the highest Phosphorus of any common livestock animal). I'd just cut it back in the fall to reduce nitrogen influx and encourage fruiting.