Here's the Alum method; found it here:
"At most any grocery store, buy a box of alum. Select a glass or
ceramic container (made for stove top use) or an aluminum pot large
enough to place your part in so it can be submerged in water. Remove
the part and bring the water up to just below the boiling point of the
water. Add alum until no more will disolve, then place your part in the
solution. Keep the solution at a simmer and you will soon observe a
trail of tiny bubbles coming from the broken drill/tap. Keep the
solution at a simmer and add water as needed as long as the trail of
bubbles continue. When the bubbles stop, remove the part and let cool
for inspection. You should discover that the steel drill or tap has
turned to a rusty mud which is easily removed from the hole."
Dave
