Stoker-man,, the Permatex Ultra-black is an automotive product. Available at auto-zone, Napa, just about any autoparts sales department,, maybe even Walmart's auto department.
I've used regular clear silicone caulk too,, not one leak.
Like Yanche said,, clean the threads first to remove oil,, and a thin layer in the female threads, and more on the male threads..
I've used the expensive 'contains teflon' white pipe dope, and teflon tape, and both together,, and have not had 100% success.. and the leaker always seems to be about 6 fittings down from the closest union... GRRR.. so I quit with the pipe dope and tape..I use exclustively RTV,,, and have 100% sealing.
Just my experiences.. maybe if I was a full time pipe fitter I could do better with tape and dope.. but I like to do it once,, not twice or three times.. plumbing boilers that is..