We had a hen recently exactly that way. She seemed fine, then, suddenly, she started acting sick; wouldn't eat; we finally caught her and when I picked her up I was appalled at how much weight she'd lost, and watery stuff just poured from her nose. I mean, like you said, it just about soaked me. A day or two before we had another hen die without any apparent symptoms except SBS for a day or two. Don't know if the two conditions were related, but we put Snowflake (with the watery discharge) in our hospital pen, and ordered her some Tylan, but she died next day. I'm pretty sure it wasn't impacted crop. Someone suggested MG/MS; someone else suggested maybe Coryza...which, by the way, can have lots of water nasal discharge...whatever it was, we disinfected everything we could with Oxine, and were blessed with a spell of very hot, sunny, dry weather. Two weeks later now, and no other sick birds...still keeping our fingers crossed. I'd try some injectable Tylan if I were you, and order some water soluble for the others, in case whatever it is spreads.