I would like to insert some short lengths of 3" copper into a DWV main line that is made of PVC. I will be wrapping soft copper around these short lengths and running the cold water feed for the shower through the soft copper to capture heat from the drain water.
My question is for you plumbers, what procedure would you use to insert a fitting or Tee into an existing run?
After I cut it, I can probably move the line an inch or so fairly easily but any more will be more complicated but can be accomplished.
Edit: I should add that the shower drain is too tight to the main line to put the heat exchanger in the 2" shower line.
If I wanted to add a Y into the main line and move the shower drain I would still have to cut the DWV and insert the Y. How do you guys cut in to an existing line to add a fitting? Do you use rubber couplings?
Would something like this be reliable for decades to come?