Step 4 · Cut Drain Pipe to Correct Height
The new PVC flange must sit flat on top of the finished floor. Dry fit your new flange, a short piece of PVC pipe, and the flexible coupling to determine the correct height. In many cases, the old cast iron pipe will be too tall. Measure and mark a cut line on the cast iron pipe, typically about 1/4 to 1/2 inch below the top of the finished floor. The best tool for this is a rented cast iron snap cutter, which makes a clean, straight cut. Alternatively, you can use an angle grinder with a metal cutoff wheel or diamond blade. WEAR a dust mask, hearing protection, and safety glasses if using a grinder.