A main pool drain leak can be a repair technician's nightmare. The pool usually has to be drained completely, and the job involves destroying concrete and plaster to expose the leaking section so it can be repaired. Although it is called the main drain, it's not a drain at all. It's an intake pipe that leads to the pool pump, and an important part of the circulation system of the pool.
Step 1: Locate the Leak
Use a leak detection service to pinpoint the leak. These services will save hours of time and a lot of money, as they have the experience and tools to locate these leaks.
Step 2: Chart the Main Drain
The main drain is a 1-inch to 2-inch line leading from the bottom of the pool, outside the pool shell, to a trench about 24 inches below ground level. The drain joins other pool lines from the skimmers and the return lines. The skimmer and main drain lines join into one that leads to the suction side of the pool pump.
Step 3: Empty the Pool
Turn off the circuit breakers and power to all the pool equipment. Using the submersible pump, drain the pool completely. Use the buckets to scoop the last few inches out. Use a cup to scoop out any water in the main drain well after you remove the main drain cover. The bottom of this well should be dry for the repair.
Step 4: Expose the Main Drainpipe
Push a length of wire into the opening of the intake pipe to determine the direction it runs in. When you know where the line runs, mark the area and excavate an area 24 inches wide, centered over the main drain pipe, so the pipe is exposed.
Step 5: Breakaway the Concrete
Break out the leaking area with the jackhammer. The leak will probably be at a joint that has been improperly glued. This leak will probably be under the main drain well or within 2 feet of the main drain, where it makes its turn towards the trench.
There may be a grid of rebar under the pool plaster, which you will need to cut with bolt cutters.
Step 6: Fix a New Pipe Section
Using the chisel and hammer, break away the concrete around the pipe. Clean up the debris.
Locate the leak and cut out the entire section above and below it. Make up a new section exactly like the one you took out. Prime and glue all the parts together. Let it dry before installing it. If there is a hole under the leak, fill it with pea gravel.
Step 7: Pour the Concrete
Mix the concrete and pour it into the hole, covering the pipe. Replace the rebar and bring the concrete to 1 inch below the pool surface. Dry overnight.
Step 8: Re-Plaster
Mix the plaster compound and spread it over the concrete until it reaches the level of the existing pool surface. Trowel smooth. Install the new main drain cover. Fill the pool immediately so the pool plaster sets underwater, and make sure not to wash away the plaster while you are filling it.