Drain relining, also known as cured-in-place pipe (CIPP) relining, is a method of repairing damaged drains by creating a new pipe within the old one. This technique involves inserting a flexible liner coated with a special resin into the damaged drain. The liner is then inflated, pressing it against the walls of the existing pipe. Once the resin cures, it forms a durable, seamless new pipe within the old one, effectively sealing any cracks or leaks and restoring the structural integrity of the drain.