Pool owner going on 2 years now and haven't had much luck with hiring pool service, so I'm taking over! I'm learning a lot and recently discovered that I should have a Wier door on my skimmers and im not sure how they are plumbed. I'm attaching a few pics and would like help please! My skimmers (2 of them) have a single hole in the bottom and 2 other holes on the side. The higher hole on the side is threaded. I know the bottom center hole goes to my pump, but don't know about the others. Pool was built in the late 90s. Thanks in advance!