Hoping someone can answer this question for me. I have a 20x40 IG pool. At the bottom of the skimmer, there are two holes. I imagine one of the holes is the return to the pump. What is the other one for? And how do i winterize it? There's a plastic latch that seems to be able to block off on or the other of those holes.

Thanks!

Do you have a main drain? The second hole goes to it and the flap thing is a diverted to control suction between the skimmer and the main drain

Edited: posted response to another thread here.

Yes, i do have a main drain. So what does this flap do exactly?

The main drain goes to the pump AND the skimmer...or just to the skimmer?

Thanks!

Some builders plumb the main drain to the second hole in the skimmer, others run a separate pipe back to the equipment pad, and a few join the pipe from the maine drain with the pipe from the skimmer underground somewhere.

Having a skimmer with two holes in the bottom is suggestive that the second hole might go to the main drain, but it doesn't prove anything as many builders always use two pipe skimmers even when they aren't connecting the second hole to anything at all.

Acadian, do you have a valve for the main drain at your equipment pad as Jason described? If not then you'll need to do some tests to see if the MD is connected to the skimmer but considering that you have that flap thing it most likely does go to the MD

Yes, i have two valves going to the pump.

I will have a closer look in the bottom of the skimmer and try to see if that second hole goes anywhere.

Thanks!