Step 6 · Measure and Cut the PVC Pipe
Measure the exact distance between the two ends of the cast iron pipe. Now, take one of the transition couplings and measure the distance from the end of the coupling to the internal pipe stop. Double this measurement and subtract it from your overall gap measurement. This new, shorter measurement is the exact length to cut your PVC pipe. Mark this length on the Schedule 40 PVC pipe and make a straight cut using a PVC cutter or a hacksaw. Deburr the cut ends of the PVC pipe.