Fernco 1006-44 1006-44 4 in. Concrete x 4 in. DWV Flexible PVC Coupling

The Fernco 1006-44 is a transition coupling that joins 4 inch concrete pipe on one end to 4 inch DWV pipe on the other. The two ends are sized differently on purpose, since 4 inch concrete pipe has a larger outside diameter than 4 inch plastic DWV, so the sleeve is stepped to take both. Point the correct end at the correct pipe when you set it.

That is exactly the job it is built for. One end takes 4 inch concrete pipe, the other takes 4 inch DWV plastic, so it bridges an existing concrete sewer or storm lateral to new PVC or ABS DWV pipe without needing a mortar joint. It is a flexible coupling, so it also absorbs the small misalignment you usually find between an old buried line and new pipe.

Order Fernco 1006-44. That is the manufacturer part number, and the second half of it reads as the two sizes, 4 inch by 4 inch, with the concrete side and the DWV side matched to the same nominal size.

No solvent cement and no mortar. It is a flexible sleeve coupling that slides over the two pipe ends and seals by compression when the bands are tightened, so it goes together with a driver or socket wrench and can be taken apart later if the line needs work. Clean both pipe ends and set them to the internal stop before tightening.

For joining dissimilar pipe underground, the flexible coupling is the practical choice: it takes up the diameter difference between 4 inch concrete and 4 inch DWV plastic, tolerates slight angular misalignment, and does not require the pipe ends to be perfectly square or the same material. A rigid fitting only works where both pipes are the same material and diameter and can be held in alignment. Where you are transitioning materials in a trench, use the transition coupling.