Sealing Black Iron Pipe Joints Video
This pipe has threaded fittings at the connection point which need to be sealed with pipe dope or Teflon tape. The machined threads are not perfect, thus the need for sealing. Teflon tape should be wrapped onto the male end of the pipe in a clockwise direction when looking at down the end of the pipe. Once the Teflon tape is in place, screw the joint together. After hand tightening, use pipe wrenches to complete the assembly.
An alternative method of sealing pipe joints is the use of pipe dope. Pipe dope has the consistency of mashed potatoes. You just paint in on to the male threads of the pipe. Then, screw the parts together and tighten with pipe wrenches.
Two cautions! Do not put any pipe dope inside the black iron pipe and do not put Teflon tape inside the pipe either. Secondly, be sure to use those pipe wrenches to fully tighten the joint. Hand tightening alone will not work.