I have a 3 inch pvc drain pipe i have to move 4 inches that is embedded in concrete. I have hammered out the concrete and now im ready to cut into the line and put a T coupling in for a toilet. My question is, how do you install the t coupling in the concrete? I can easily glue it in on one side, but since the other end of the 3 inch pipe is in concrete as well, how do I draw the two pipes together to seal the the gap?
It is not ideal but you can bury it in concrete. If you have enough room you can use what is called a repair coupling. It is a coupling with no stop in the center. Slide the repair coupling on the longest accessible side. You would glue a 2" stub in the end of the Tee facing the repair coupling, mark the pipe in the floor with your Tee set up, and cut it on your mark. Glue the Tee on the opposite side of the stub and slide and glue the repair coupling over where you cut the existing pipe up to the Tee.
You might need a flexible PVC coupling.
Say you cut the old pipe to (left side old pipe) - (gap) - (right side old pipe), then install as (left side old pipe) - (T coupling) - (short new pipe) - (flexible coupling) - (right side old pipe). Here you can use the cut-off pipe segment as the (short new pipe).