Important note about tubing... You must tube just fluids first, and I would start with 60ml, wait 60-90 minutes and repeat if crop has mostly cleared, then maybe one more time in 2-4 hours. This amount should have his organs and intestines working better, which will help him process food. Once...
Orbax is in the same family as Baytril, so it's a good one. If you want to learn how t tube I can teach you. It will save you lots of time. All they need is tubing twice a day, and once you learn, it will take you less than 5 minutes to do it.
-Kathy
It's possible, but I can't help but wonder if the tissue under the pus looked cancerous to the vet. Interestingly, I think I have a chicken with something similar. She has a lump in front of her trachea that's covered in pus. Each day I remove it, and the next day it back.
-Kathy
Injectable or powder? Neither will help the pus go away, but might be okay once you get the pus out. Trust me, you have to be the pus out. No point in giving drugs until you do.
-Kathy
Duh! Yes, could also be wet pox. Had that here in 2013, but only the chickens had it. Definite possibility if the OP still has mosquitoes around.
-Kathy
Another possibility is canker. Canker is common in pigeons, but not as common in poultry. Treatment for canker is metronidazole or something similar. Really would be best to consult with a vet. Whatever it is, it's likely to need drugs that one can't get at a feed store.
-Kathy