I am installing a new basement shower. Drain is 3" cast iron, cut off 2 1/2 inches below cement floor with about an inch of space around it to work outside the cast pipe if I need to. Drain for new shower is 2" pvc. I need 2 inches below the cement floor to install the pvc shower drain connection. Local plumber suggested that I install a 2 inch pvc coupling inside the cast pipe and secure it in place using PC 4 (a cold caulking compound) - sort of a rope with a type of cement in it. I've never used this product before. Any suggestions?
In new house construction up here, the plumbers rough in the basement for a bathtub they block out the drain area for future work, but if the bathroom isn't on the list for completion they allow the concrete to be pored around the pipe. When they come back to work at it later they jack hammer around the pipe so they can make connection. I am surprized your plumber would suggest an answer from 30 years ago.