Vent disease takes long-term antibiotic therapy to eradicate, not just a shot or two of bicillin. With a kit, I would consider culling. And I would also consider where it got the disease from... most likely its dam, and that means that all the others have been exposed, and it is active in the rabbitry where they are being housed. At which point, some thought and discussion should probably take place.
You are generally looking at treating vent disease with injections of bicilln every other day, and this must be maintained on a diligent schedule for two weeks AFTER symptoms disappear.
At breeding time, I carefully inspect the doe as well as the buck whom are going to be bred for any and all health problems, including vent disease, ear mites, fur mites, eye problems, etc. For most of us who have more than just a few rabbits, this is the only time we really do hands-on with our breeding stock. I also worm and clip nails on bunnies at this time.