Leak

[Scooparama]

I have a System 3 filter system. On the return line, theres a 3" return pipe that sends the filtered water back into the pool. Additionally, there is a ¾" auxiliary line that returns water to the pool. It has a leak. I simply shut the valve off to stop the leak, but I'm not sure what this smaller line is for. It feeds into a small well that has an overflow tube inside. I would post photos, but there doesn't seem to be a way to do that here.