A builder here in south Texas used the long Baker Hydro skimmers that are about 3 to 4 feet deep. I need to plug the opening at the very bottom to do repairs at the pump which is below the grade of the pool. I have tried 1.5" and 2" threaded plugs and nipples, but can't get them to screw in. Is anyone familiar with these skimmers and what can be used to plug the bottom.