Hello, I'm Dr. Diane and will try to help you. Removing the visible maggots one by one when they come to the surface is one method (although slow and tedious) to remove them. Sometimes flushing the area with saline or dilute disinfectant solution helps to get them out, which your vet may have done as well. Some vets have had success killing them w/ Capstar (a pill) or Ivermectin (but a different dose than the heartworm preventative). I would keep a close eye on your dog, keep him inside as much as possible to prevent re-infestation, keep the area around the rectum clean and dry, and if you see any maggots that you cannot remove manually or flush away with saline, then take him back in tomorrow and ask about treating him with Capstar or Ivermectin. Many dogs are also treated with antibiotics if they have open sores.
Hope this helps and please let me know how he makes out tomorrow!
The vet has given an injection to kill the maggots that might have gone in. However im curious to know if I will be able to see the dead maggots in his poop. I want to check that they are actually coming out. Also if I need to check his stool