Admittedly, I'm a novice when it comes to owning a pool. Recently, I noticed the water flow from the pool pump is reduced and the filter pressure is high (30 psi). I have a standard Pentair system. Anticipating that the filters probably need cleaning, I went to open the air relief valve (with the pump off of course) as the first step and water came out and continued to come out even after draining 50 gallons. Is this an expected outcome with a pool that is situated higher than the pump? I watched a few videos about filter cleaning and in each video only air comes out of the air relief valve. I've only owned the house for less than a year so I don't know how it "usually" is.