Mystery PVC Pipe among pool equipment

[Jinro1]

Hello, I moved into the house this summer and am an experienced pool owner however, I have no idea what this PVC pipe does.

In the picture, it's the long straight PVC pipe in front of the filter. it has an opening at the top and is filled with water.

(don't mind the ziptie and tape at the top - it was a mosquito breeding ground so i have a mosquitor dunk hanging from a zip in the water) I've also found a frog in the pipe once but don't know what happened to it since.

Anyone know what this pipe is or does? the water inside does not seem to react with any of the pumps or valves. level doesn't really change and as far as i can tell the water seems stagnant.

Thank you for your help!

 

[Jimrahbe]

J,

I have no clue, but I suspect that @JamesW knows what it is for...

Thanks,

Jim R.

 

[JamesW]

I don't know.

Maybe stick a garden hose in it to see if water flows out anywhere.

 

[ccbill]

Have you tried to suck the water out of it to see if the level returns?

 

[vtpools]

What type of pool do you have? Could be a trouble water pipe for removing groundwater from behind a liner. I would also say it could be a polaris line that was put in during installation but never hooked up, but it looks like you already have one installed..