How to Repair a leak behind the bathroom tub wall
First you have to expose the leaking pipe by taking out the section of the wall where the leak is. The most common pipes you will find behind the wall are polybutylene and cpvc. Polybutylene pipe has plastic fittings that can break and it develops pin hole leaks easily. Cpvc is rigid and breaks very easily. All you need for this project is a plastic pipe cutter. First remove the old water line. Attach the new supply line to the faucet connector. Then cut the supply pipe off so that the remaining pipe comes about half way up the new supply coupling. Then push that supply up into the new coupling until it is up in the coupling and really tight. Now you are ready to do the other side. Just repeat the steps on the other side. The new supply lines are color coated red for hot and blue for cold. Just repeat the steps on the other side then turn the water back on so that you can check for leaks and you are done.