Installing a Mission coupling
When repairing a section of pipe in an existing run, don't try to cement (solvent-weld) all the new couplings. Most drain systems use rigid pipes fairly large in diameter. You can't flex them enough to slide on that last fitting and get it to seat fully. Rather than struggle with cement, pros use a “mission” coupling (Photos 3 and 4) that clamps over the last joint. Even though a mission coupling costs more than a plastic coupling, the extra cost is worth it. Sometimes, pros will even use two mission couplings in tight situations. Photos 1 – 4 walk you through the process. Be sure to buy couplings with full steel sleeves, and make sure mission couplings meet code requirements in your area.