Going to paint my pool this summer. Last time I painted my pool a pool company fixed some loose concrete around my main drain. I remember when he removed the pressure plug in the main drain he screwed in about a 4ft piece of pvc where he unscrewed the plug. He said this will keep the ground water out while you paint. Is that a safe method to help with the ground water pressure? Also what size fitting would I get to screw into the main drain mist likely? Thanks