Originally Posted by KULTULZ
Well, I must respectfully disagree with your position.
Source- -NPT EXPOSED-
Your example is certainly straight thread. It needs no sealant as the machined seat makes the actual seal.
And I agree with everything you've posted this time. Of course, you didn't say NPSM in your original post, you said NPT, which conventional usage would indicate is a tapered thread. I also was not advocating applying sealant to the treads of a straight thread brake bleeder (which I suspect you will find is a standard machine screw thread). I agreed with your post that air will leak past the threads of a loosened bleeder screw. My whole point was that I've found that a dab of grease around the bleeder where it enters the wheel cylinder or caliper will prevent this air leakage and helps with using a hand-pump vacuum bleeder tool. The pressure differential is small enough that there is little risk of actually drawing the grease into the brake fluid, and even if you did, you are sucking this fluid out of the bleeder screw anyway. The grease would need the upstream swimming capability of a sex-crazed spawning salmon to be able to migrate into the brake system.