When you are making up your soaking solution of water and epsom salts, make sure the water is as hot as you can get it but still able to hold your hand in it and then stir in the epsom salts until they are no longer dissolving in it. The epsom salts are more effective like that, they will draw out the infection better. I remember reading somewhere that the water has to be completely saturated with them and when they no longer dissolve in the water that is when you know it is saturated.
Animalintex poultice is also a really good drawing poultice. You can buy them in pre cut hoof shapes, but it is a bit cheaper to just buy the regular rectangle shape pad and cut out your own.
Movement is also important to keep the circulation going, so if your horse is able to be turned out as much as possible to move around that's great. Hand walking can also be helpful. You could hand walk him each time you soak. Just be sure to keep him on nice footing like in an arena or on grass so it will be more comfortable for him.
You can soak 3 times a day if you have time, but 2 is sufficient. Also, once the abcess bursts, I like to soak for a couple of extra days after just to make sure it is all drawn out before it closes up.
I hope this can help and that your horse feels better soon.