In this video, This Old House plumbing and heating expert Richard Trethewey makes watertight connections.
1. Seal plastic fittings by wrapping the thread with Teflon tape. Go around the fitting two or three times, then pull the tape tight to break it off.
2. On metal tapered fittings, coat the threads with paste-type pipe sealant, also called pipe dope. Brush the sealant onto the threads all the way around the fitting, then assemble the joint.
3. To increase the water-tightness of a plumbing connection apply pipe sealant and then wrap wicking (string) around the threads before assembling the joint.
4. On a ground joint apply, pipe sealant to the unthreaded portion of the joint, but don't apply any sealant or Teflon tape to the joint's straight threaded connection.
5. If a straight threaded connection has a rubber gasket, there's no need to apply pipe sealant or Teflon tape. Simply tighten the connection enough to compress the gasket.