A leaking shower drain can occur due to a variety of reasons. The most obvious reason is that there is a crack in the shower drain that requires you to fix that section of it in order to stop the leak. It's important to determine whether the leak is caused by damage to the shower drain or if it is because the tub seal is compromised.
Step 1 - Ensure the Leak Is From the Drain
To make sure your leak is coming from the shower drain and not from a compromised seal between the bathtub and the floor, use a funnel and pour quite a bit of water directly down the drain. Look for the typical signs of leakage. If none are visible, fill the tub and look again for leaks. These tests should identify the source of the problem.
Step 2 - Create an Access Panel to the Shower Drain
Go to where your shower is located and find where the pipes are that lead to the shower. They should be under the flooring or above the ceiling in the floor below the drain. Place a drop cloth or metal pan on the floor in order to catch any water that may leak when you cut an access to the drain. Wearing safety glasses, use a drywall saw to cut a panel in order to gain access to the pipe. Remove the piece carefully in order to be able to place it back where it belongs after you complete the repair of the shower drain. You may have to access the plumbing through a closet, attic, or even a bedroom.
Step 3 - Remove the Leaky Part of the Drain
Find the source of where the water is leaking. You'll usually notice a discoloration or dripping where the leak is coming from. Use pliers to remove the portion of the drain, whether it be the gasket, drain body, or strainer body. Remove the strainer with a screwdriver, and remove the gasket and other parts with a pair of pliers.
Step 4 - Patch or Replace the Shower Drain
When you purchase a shower drain repair kit, there should be instructions that will help you to dismantle and reassemble your shower drain. You only need to repair the part of the drain that is broken if all of the pieces still fit together, using a combination of old and new. Reassemble the shower drain and make sure all pieces are securely in place.
Step 5 - Test the Drain and Replace the Drywall
Test your leaking shower drain by having turning on the water in a small stream. Check the pipe downstairs to see if any leaks develop. If there are no leaks, patch the wall using the drywall mud and mud knife. At this time, you should also cut away and remove any piece of ceiling that has water mark damage from the leak. Use extra drywall and the drywall mud to replace the necessary portion of ceiling.