\nBuy a shielded transition coupling listed for 1-1\/4 inch plastic or steel
\nto 1-1\/4 inch copper. A Mission K-1125 style coupling is the kind to ask for.
\nMeasure both pipes before you tighten them.
\n<\/strong><\/p>\n
Why The Size Looks Strange<\/h2>\n
Your copper pipe is not measured like a PVC pipe.<\/p>\n
That is why the numbers do not match.<\/p>\n
A 1-1\/4 inch copper drain can measure about 1 3\/8 inches outside.<\/p>\n
A 1-1\/4 inch Schedule 40 PVC pipe can measure about 1.66 inches outside.<\/p>\n
So, do not buy only by the name on the package.<\/p>\n
Buy by the pipe material and outside diameter.<\/p>\n
Use A Shielded Coupling<\/h2>\n
A plain rubber sleeve may seem easy.<\/p>\n
But a shielded coupling is usually the better choice indoors.<\/p>\n
The metal band helps keep both pipes lined up.<\/p>\n
It also helps stop the joint from sagging.<\/p>\n
This matters on a bathroom sink drain.<\/p>\n
That drain still needs a steady slope after the repair.<\/p>\n
You can read more about shielded couplings from\u00a0Fernco<\/a>.<\/p>\n Ask for a shielded copper-to-plastic DWV transition coupling.<\/p>\n Tell the supplier your actual pipe sizes.<\/p>\n Say the copper is 1.375 inches outside diameter.<\/p>\n Say the PVC is 1.660 inches outside diameter.<\/p>\n Mission Rubber lists K Series couplings for copper and plastic drain use.<\/p>\n You can compare the style at\u00a0Mission Rubber<\/a>.<\/p>\n Cut the copper pipe square.<\/p>\n Clean burrs from the cut end.<\/p>\n Dry fit the PVC before gluing.<\/p>\n Keep the pipe slope aimed toward the drain line.<\/p>\n Tighten the coupling bands to the listed torque.<\/p>\n Do not guess with a screwdriver.<\/p>\n Use a small torque wrench when possible.<\/p>\n For code details, check your local plumbing office. The right part is not just a rubber coupling.<\/p>\n It should be a shielded transition coupling.<\/p>\n It must match copper on one side.<\/p>\n It must match PVC on the other side.<\/p>\n When in doubt, bring pipe samples to the supply house.<\/p>\n I’m Chris Mayer, writing for Plumbing 101<\/a>.<\/p>\nWhat To Ask For<\/h2>\n
Simple Repair Tips<\/h2>\n
\nYou can also review model plumbing code resources from\u00a0ICC Digital Codes<\/a>.<\/p>\nFinal Takeaway<\/h2>\n
![\"Fix](\"https:\/\/plumbing101.i234.me\/wordpress\/wp-content\/uploads\/2026\/05\/Fix-Copper-to-PVC-Sink-Drain-Leaks-300x169.png\")