During a renovation, a plumber needs to connect a new 50 mm (2 inch) PVC drain line to an existing 100 mm (4 inch) cast iron stack. The connection must be watertight and allow for thermal expansion and contraction. Which method is most appropriate for this transition?

Question: During a renovation, a plumber needs to connect a new 50 mm (2 inch) PVC drain line to an existing 100 mm (4 inch) cast iron stack. The connection must be watertight and allow for thermal expansion and contraction. Which method is most appropriate for this transition?

Answer options:

• Solvent cement the PVC directly into the cast iron hub. ✅ Use a rubber repair coupling (Fernco type) with stainless steel clamps.
• Thread the PVC into a tapped opening in the cast iron.
• Melt lead and oakum into the cast iron hub around the PVC pipe.

Correct answer: Use a rubber repair coupling (Fernco type) with stainless steel clamps.

Explanation: A rubber repair coupling (often called a Fernco coupling) with stainless steel clamps is the most appropriate method for connecting dissimilar piping materials like PVC and cast iron, as it provides a watertight seal and accommodates minor movement due to thermal expansion/contraction. Solvent cementing or threading PVC directly into cast iron or using lead and oakum with PVC are not code-compliant or effective solutions.