In the picture, the two valves to the left control water coming FROM the pool to the pump. One is undoubtedly the skimmer, the other is from the low drain(s). The two on the right are for the returns--filtered water coming back to the pool, after passing through the in-line chlorinator. The pipe coming directly out of the right side of the filter and going straight into the ground is your backwash drain line.
Hope this helps.
Carl
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