Quote Originally Posted by BuffaloJohn View Post
2 - Actually they cut into fully live pipes like that all the time. There is a special saddle they put on the pipe. There is a special fitting that is a combination of drill, fitting, and coupling that are part of the assembly. You make the hole into the larger pipe and it is capped auto-magically... You hitch up the tap pipe and remove the saddle assembly, all without making a mess. I have watched the tapping of PVC and asbestos concrete pipe for the water system my house is attached to.

All this was done, in each case, without depressurizing the main. Main was about 110psi, 6" to 8" (depending on the job and branch). Barely a drop spilled...
Its even done on large high pressure live natural gas pipelines. You might think it is crazy, but a welder will weld a collar or a flanged coupling to the pipeline then a valve is mounted and the special penetrating device makes the hole in the main pipe.