We just bought a house with an above ground. from the research i have done it is approx. a 9000 gallon pool. It has a waterway sand filter. I have connected all the hoses and have filled the pool half way between the min and max markers. When i turn the pump on I can see the water filtering into the pool, but at the back of the filter there is water pouring out what looks like a threaded drain pipe, located at the bottom back of the filter. Is this normal? does this drain require a cap? I am sorry but I have never done anything with a pool before. I tried searching the forums, but honestly have no idea what I am looking for. Any help would be appreciated.