With the abscesses on my alpacas (which are blessedly few!) here's what I do:
First off keep them open! Pulling off the scabs isn't exactly fun, but necessary.
Get some betadine (a big bottle) not the strong stuff, but the strength used for first aid.
Get some 12 CC syringes, no needles needed!
Get a person to hold the animal!
Hot compresses can help to loosen things out, but use a syringe full of betadine and squirt it into the abscess. Try and work out as much puss as you can. Sometimes you can squeeze a bunch out. Sometimes the puss has become granulated (congealed) in the middle and if you can get ahold of part of it with a paper towel you can pull the granulated part out.
Keep flushing with betadine and working as much puss out of it as you can, particularly if there's granulation.
If it's a larger abscess my vet has had me put gauze squares soaked in betadine inside of it to help keep it open so it can heal from the inside out. (thankfully I only had to do this once and it wasn't on my animal or even on my farm!)
I would clean up the puss and do a good flush with betadine twice a day if you can. The first good cleaning is critical though. If there's a granulated chunk of puss inside of the abscess it's going to be very hard for it to heal.
As it begins to heal the skin and tissue around the abscess (which is probably almost rock hard right now) will start to soften. You will be able to manipulate the abscess more easily, and obviously the amount of puss will decrease.
Some people like to use Swat or something similar to keep flies off. Other people use fly spray, other people don't care.
Good luck. Let me know how he does! Feel free to PM me if you have any trouble. I'm not a vet by any means, but I've treated a few abscesses of various degrees and on a variety of animals.
Kendra