I have been asked by my customer to install 2nd drain on the bottom of her pool. I will need to cut about 5 feet long x 12 inches wide x 16" deep block of concrete from the bottom of the pool, excavate and expose existing drain pipe, split the drain into two and install two drain heads. Now, how do I repair this hole in the bottom of the pool so the pool doesn't leak after refilled ? Appreciate your responses.