P.S. Should I just leave it (topically speaking) other than cleaning it? The vet (a friend) said it's better to leave it (i.e. not bandage it up) - but he keeps scratching it every time a pus-y scab forms on it. Then it bleeds again.

When it starts to crust over with pus - the pus is thick, oozy, smelly (it's BAD - you can smell him 3 ft away from you). It nevers dries enough to be crusty, I mean. It's still wet. The colour is opaque-yellowy-greeny-grayish. Blegh, it makes me gag thinking about it.