Best Way To Seal Threads To Prevent Air Leaks?

[ebelp]

I used Permatex Thread Sealant on my build and I have zero leaks.

[Shmee]

Permatex or Loctite sealant are the best.

When it comes to cars, or anything carrying a fluid other than water, it is best to use a sealant over a tape.
Teflon tape can break down in the presence of oil and/or glycol causing leaks over time; and on components that require a ground, teflon tape cause incomplete grounding where as a sealant provides a good grounding.

Once cured, sealants typically also have a higher yield strength than tapes.