I just opened my pool and got everything running, but am confused about something. I bought the house last year, and had the pool winterized by a company. In the process of de-winterizing, I pulled a plug out of the side of the pool that I didnt remember being there last year (I think it was plugged with a white plug last year). When I turned the heater on, I put my hand next to it thinking it was putting water into the pool, and it practically sucked my hand in. My confusion is that I have connections in the skimmer basket for the vaccume, which is what I used last year. Can someone explain this to me? I gather it is a dedicated line, but I just want to figure out how pools are typically plumbed (ive done some reading/searching for the past 30 min, but am still confused).