I've been troubleshooting a spa leak. Have it narrowed down to the main drains/suction line for the source of the leak. While troubleshooting, I pulled the drain covers off and noticed these 2 holes with no plugs. Should these bottom threaded holes be plugged? I am noticing that when my spa is fully drained, a few inches of water will find its way back in through these main drains. I'm assuming this is ground water and not sure if it's coming in through these bottom holes or if it's coming in through a line leak to the main drains. Any ideas or knowledge with these open threaded holes down there? I've attached a picture without the covers on. Thank you