Sorry for stupid question, but why is it draining? Is it open cut?
Swelling takes FOREVER to go away. My horse got hit between her legs, had HUGE hematoma, and now after almost 4 weeks she still has bump there.
If he's not obviously in pain I wouldn't put him in stall: moving actually helps the hematoma to dissolve more quickly.
Next one is applicable only if you have closed hematoma (no open wounds, cuts, etc.):
HOT compresses together with massage do help a lot. I knew it before and my vet (as well as another vet I talked on the phone) recommended me to do that right on spot (usually you start it 2 days after the incident).
I also used the liniment from Horseman Dream with camphora and that seemed to help a lot too (it keeps the area warm and again speeds up the dissolving of hematoma).