Also note, since you are working with a TAPER pipe tap, you NEVER run it in all the way as you would a regular bolt thread tap!
As a general rule, always stop with a MINIMUM of 6 threads showing above the surface of the hole you are taping.
You can then try screwing in the fitting, see how deep it goes before getting tight. You can then tap deeper if necessary. But if you go too deep...
PS: Check your thread pitch carefully. There are at least 2 different thread pitches (NPT and BPT) that are very similar. NPT is the most common, found on American made products, BPT found on most imported products.