From the Vet -
Occasionally those brisket calluses become infected and do this. I would clean it on the outside with a disinfectant such as Nolvasan (chlorhexidine) scrub (preferred) or Betadine scrub once per day (wear gloves). You could flush off the soapy scrub with Vetericyn spray or use dilute Nolvasan or Betadine solution in clean tap water (just a little squirt into about a liter of water). All of those products are available over the counter - Co-op or Tractor Supply or Southern States. I would also treat with injectable antibiotics such as Biomycin -200 @ 4.5 ml per 100 lbs SQ or Nuflor @ 6 ml per 100 lbs every 4 days for 10 - 14 days.
If there is a big abscess pocket (which I doubt given the amount of drainage - I suspect any pockets are already draining) we would lance it and flush it with the same Nolvasan solution mentioned above.
ETA: It turned out that just shearing him was enough to dry it out and clear it up. By the time I had the vet out on Thursday to look at him, he was healing and mostly done with the entire mess. The vet was amused at me.