I'm sorry his injuries are so serious. You could consider giving a systemic antibiotic. Penicillin G is typically recommended for wound and tissue infection. You can get it at many farm stores. It helped saved the life of one of our hens after a hawk attack. It does require an injection, which is not too hard to do.
It sounds very infected, so I think those antibiotic injections are the route I would go, too. Is the pus getting thick and goopy, like it might be drying on his face? If it is I'd try holding a warm damp washcloth on his face for a few minutes just to loosen up the gunk.
I would not force it on him. I would add electrolytes to the water, and apple cider vin., etc like Amiga said above.
I used a couple of chamomile tea bags in warm water in a bucket & dunked my duck's head when she was holding her eye closed (thanks, Amiga!) and then treated her with Vetericyn. I got it at my TSC & it was easy to apply & not terribly expensive.
It is a good, all around product & should help fight infection, abrasion, and clean the eye, too.
I would think lots of warm baths & limited access to foreign objects - dirt, hay, grass, etc. would be best.
Good luck, poor little ducky.
ETA: You could feed mashed peas, or mashed potato. That might entice him- if he is anything like my ducks, he won't be able to resist.
Thanks. Yesterday we got him to eat and drink a lot. He was very hungry and thirsty. Today he seems much more calibrated and is getting up and walking around in his pen. His eyes aren't producing as much pus, if any at all. They look much better.
I had an old Toulouse goose that finally went blind (21 years old.) Our Pekin hen was the only other bird left with her. The Pekin kept Lucy company for about a year, acting as a "seeing-eye-duck." She led her to the grass when turned out in the morning, kept track of her throughout the day, and led her back to their pen at night. The duck went about her busy pecking, swimming and nosing around, but kept a duck-ear out for the goose. Very heart-warming, what one critter will do for another.
I think the Pekin hen will be a comfort for your injured boy. I would leave them together unless the hen becomes aggressive toward him. I bet she will "mother" him somewhat if they wander around in a safe area together.