A leaking main drain in an in-ground swimming pool is often a pool repair technician's worst nightmare. It usually means draining the pool completely and breaking through the plaster and concrete around the drain to expose the leaking section of pipe and repair the leak. Though everyone calls it the main drain, it really is not drain at all, but an intake line that leads up to the pool pump. It's an important part of the pool's circulation system.
Identify the nature of the problem with the main drain. A good leak detection service can pinpoint the leak, saving hours of time and perhaps hundreds of dollars searching for it on your own and breaking up concrete in several suspected areas. The main drain consists of a 1-1/2 or 2-inch open line leading from the bottom of the pool up outside the pool shell to a trench about 24 inches below ground level. Here it joins other pool lines from the pool's skimmers and return lines. The main drain line and the skimmer lines join into one line that leads to the suction side of the pool pump. If the leak is at the bottom of the pool in the plumbing around the area of the main drain, you will have to empty the pool.
Turn off the circuit breakers for all the pool equipment. Be sure the pump, heater, underwater pool lights and any other piece of equipment that operates the pool will not come on while the pool is empty. Drain the pool completely with the submersible pump. A few inches of water will remain in the bottom after the submersible pump quits working. Use the buckets to scoop out the remaining water. Remove the main drain cover and use a cup to empty the main drain well. Get the bottom completely dry for the repair.
Determine which direction the intake pipe runs by pushing a wire into the opening and feeding it a foot or two into the pipe to determine direction. Once you know where the line runs, mark the area to cut. The excavation area should be 24 inches wide, centered over the main drain pipe and as long as needed to expose the pipe.
Use the jackhammer to break out the leaking area. With PVC line, the leak will most often be at a joint that was improperly glued during construction. This joint will often be directly under the main drain well or within 2 feet of the main drain where the line makes its first turn up toward the trench. The concrete (gunite) under the pool plaster has a grid of steel rebar embedded in it to strengthen the pool shell.
Cut the rebar with the bolt cutters as you expose it and bend it out of the way to get to the pipe and joints underneath. Use the hammer and chisel to carefully break away the concrete around the pipe and expose it completely. Clean up all the debris before continuing to the next step.
Locate the source of the leak and cut the line at a point above it with the reciprocating saw. Remove the entire section below the leak and make up an exact duplicate of this section with the new PVC and joints. Prime and glue all the new parts together and let them dry thoroughly before installing them. If the line has been leaking for a long time, there may be a void under the pool shell where the water has washed the soil away. Pack this void with pea gravel to support the repair patch.
Make sure the replacement pipe lies in the same manner and depth as the original section. Mix the concrete and pour it into the hole, covering the pipe. Bend the rebar back into place in the concrete and make sure the concrete completely covers it so it won't rust through the new pool patch. Bring the concrete up to 1 inch below the existing pool surface and let it set up and dry overnight.
Mix the pool plaster patching compound and spread it over the concrete. Bring it up to the level of the existing pool surface and level and trowel it smooth, feathering the edges to match the pool surface. Check the opening in the pipe to be sure no concrete or plaster patch has fallen into it. Set the new main drain seating ring into the fresh plaster over the main drain well. Carefully install the new main drain cover onto the ring.
Begin filling the pool immediately. The plaster patch needs to set up underwater for a smooth, crack free cure. Use a garden hose with a rag tied over the end to divert the water flow and avoid washing out the new plaster patch.