How to Tie Into Existing Drain Line

Cutting a tee or wye fitting into an existing drain line using couplers is a pretty straight forward process. Whether you’re connecting clay, cast iron, or plastic the principle is the same. Cut out a section of pipe, lay in the new pipe, and use couplers to seal the deal.

Step 1 – Cut Out Old Pipe

Remove a section of the existing pipe exactly the size of the pipe you want to add in.

Step 2 – Insert Couplings

Slide a coupling onto both sides of the remaining pipe. In this case I’m using 4×4 inch Fernco couplings available at the Home Depot.

Step 3 – Lay in New Pipe

Lay in the new pipe and mark a line on its end half the size of your coupling. Here I’m marking 2” for my 4” coupling. Slide the couplings over the new pipe to your half way mark.

Step 4 – Tighten Couplings

Use a torque wrench that slips at the required tightness to secure the couplings. Here I’m using a Pasco 5/16” wrench that sets the torque to 60 in-lbs.

Congratulations, you did it! 😎 If you have any questions leave them in the comment section below.

See me install couplings here:


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