As a farrier, I don't do invasive procedures other than at the express order of the
attending veterinarian.  The conversation generally runs something like this:

        "C'mon Tom, open that puppy up."

        "Hell no Doc, I ain't no vet, you open it up."

        "C'mon Tom, I'll buy you a beer."

        (Cut, gouge, cut, cut - SPPLURTTTT! - Stink, stink, stink!)

        "Dammit Doc, I think I got some of that nasty shit in my mustache."

        "Better you than me, sucker."

When a vet instructs me to do so, I pinpoint the location of a resolved abscess
by pain response using hoof testers, then use a very sharp gouge to remove a
narrow strip of exfoliating sole over that location until drainage is established.
The drain site is kept as small as is consistent with the maintenance of drainage
in order to lessen the probability of the sensitive sole prolapsing through the
drain site.  If I'm unable to precisely locate the abscess, I figure it's not resolved
and I don't use a foot knife as an exploratory tool.  Removable hospital plates
are a pain in the arse, but after drainage is established, if the drain site is more
than about 1/2" medial to the white line, I usually apply a plate to reduce
environmental pressure on the affected area; if the drain site is within 1/2" or
so from the white line - and it often is - I forge a bubble on the inner web of the
shoe, obviating the necessity of a hospital plate.  Medication of the affected area
is possible either way, but much quicker and easier done under a bubble.