2 sorts of Loctite.
242, blue stuff, takes about 15 minutes to dry, seals air tight but can be shifted if you need to change the fittings.
Other Loctite 638, green, smelly, bonds air tight in seconds, absolute bugger to shift if you change your mind.
Both work extremely well and no chance of bits breaking off and clogging up your air system like PTFE can.
Hope that helps.