I have a duck with a nasty eye infection, started as foamy eye and progressed. She is on antibiotics now.
I know you are looking for hands free options, but if you do notice it getting worse, I bought some sterilized saline that I flush her eye out with every four hours. The others who got foamy eye, that seemed to nip it in the bud promptly.
Anywho, as you know, replenishing their water frequently. If they are refusing to wash their heads, sometimes I just stand with the shower nozzle on my hose and gently spray them down. The one with the eye infection takes full advantage of getting sprayed down and tilts her head towards the running water. Im not sure why your ducks won’t wash their heads and do not have experience with Muscovy ducks myself. Maybe it’s a temperature thing if their faces are more sensitive?
When my ducks cough, i usually make time to deep clean their sleeping quarters and their run to remove dust, droppings, and bacteria. I would suggest adding some Rooster Booster Poultry Cell to their drinkers and have one drinker with just plain water. That has helped my birds get through seasonal changes and small colds or congestion.
I know VetRX is great for this but also involves handling.
I am sorry I don’t have exact knowledge but these things have helped me get through the tough times with my flock! I hope everyone feels better soon