I personally have no idea why there is some kind of drain hole. You did a great job of cleaning it up.. Those scotch brite pads are really good to use. Those Scotch sure are smart LOL. I use them to clean copper pipe for sweating. They do a great job and are easy to grip in my hand. Sand paper is slick on the back and hard for my fingers to grip. You can also role it and force it into a fitting for equally great cleaning. Silicone grease is a great idea. Put plenty on the O rings and any screw that tightens anything down. Even the cover that hides a screw. SMEAR IT EVERYWHERE!!