What they said. Try to find a three flute tap if you can...much less likely to break. If you have a bottom to your hole, a standard tap will push the chips DOWN into the hole. Sooner or later they build up and stop the tap. If your hole goes through into a void, the chips will fall into the void (block, head, water passage, etc)
A spiral tap will pull the chips out and let you tap to the bottom of the hole. If you have a thru hole you may still get some stuff coming out into the back side.
Pipe threads are tapered so the part jams in the tapered threads.
Not sure what you're wanting to do with the hole your tapping but this pretty well covers what I know about the subject
