I'm replacing my old pool filter. There is this closed (squashed) vertical copper pipe near the return pipe. Nothing was connected to it. It continues for several feet, then connects to a PVC pipe and goes under the slab. Does anyone know what it is? Could it be connected to sewer for backwashing? Here are some pics.
It's the pipe right in the middle with squashed end.
Here you can see it curve to the left.
And here you can see it connect to plastic pipe and go under the slab.