I have a question about Main Drain and satellite valve. and I really appreciate it if you could help me with this, so I'd like to know what it means when your MD doesn't work, and there are two hole in the skimmer? and I was told by a professional that I need a "satellite valve" for that to activate my MD. what is this "satellite valve"? I can't find anything with that name online. does this mean that one of those holes goes to the MD and by activating that we basically are connecting these two holes? I really appreciate you taking the time.