I go over how I seal threaded water pipe fittings. I’m connecting threaded black pipe. I first clean off threads on black pipe. Next I wrap Teflon tape clockwise around threads. After the Teflon I apply a small amount of pipe dope. Now the pipe can be threaded into fitting. I am finishing the supply line off my boiler. When tightening threaded pipe, never back out the pipe, turning to the left. Once the water pipe or gas pipe rotates left, a gap breaks the seal. Therefore this pipe connection will leak. Any time pipe turned to left, take the pipe apart. Then clean up and reseal the thread.
When tightening an airtight threaded pipe connection. Always stop before the angle you want to connect pipes. Tightening the threaded pipe connection this way allows you to tighten the pipe into the correct spot. If you over turn the threaded pipe fitting, this fitting must be removed and resealed.
Threaded pipe connections do not need to be tighten to where it no longer can rotate. You will feel good resistance and that connection is sealed. Any kind of threaded pipe seals the same way.