It's a filter valve issue, not a liner issue. Well... I haven't ruled out a liner leak problem, but I did find that there was a small amour of water coming out of my waste line, which is clear across the property. It was leaking enough to not notice it dripping into the grass (when water is coming out during backwashing & rinsing, it blows out all over our driveway.)

Once I shut the pump off, the water stops coming out the waste end, despite the valve being set to "filter."