New pool owner, old pool. I’m afraid to open it without knowing what it is.
It says “Charlotte” on it, must be the brand.
You can see my skimmer hole at the bottom of the picture… and why is there water on it? Could be the rain I guess. 
What it is for…I don’t know. It looks like a PVC pipe clean-out plug. Charlotte is a PVC brand. It’s hard to tell size, but it looks like a 3 or 4 inch clean-out. All my piping is 1-1/2" so that is rather large.
Obviously water leaking in from above. That shouldn’t be a worry.
Anyone else have this at your pool or have any thoughts?
Thank you for your reply!
They went all out to make this look exactly like a skimmer hole, same cover style and everything. So it must be important. The pool light is in that area under the water. Being square, you can obviously open it with the “square wrench” thing, and opening it would answer what it is for… but I don’t want to open it without knowing what it is because what if it’s something like a static water pressure plug (instead of a valve) or who knows. I hope someone can recognize it by sight and know what it is.
Is that pipe 4, 6, or 8"? Maybe it is a “shaft” to be able to pump water out from under the pool so as to be able to drain the pool and not worry about hydrostatic pressure lifting the pool
Or possibly a sewer cleanout for the pool pump or pool house?
Hi,
Open it with pool motor off. That way you’re removing any possibility of pressurizing what’s under that cap. You have to realize that if it does have water in it, the water level is going to be no higher than that of the skimmer. It’s likely not under any kind of pressure, but once the caps off flip on your motor and see if it feeds that pipe. If water begins to gush out w/motor on turn it off, let water settle and screw the lid back on. If nothing happens then there is no connection between the pump and that pipe when the pump is in its normal running state. Now aligh your valve line set to its backwash position with pool off and again, turn the pump on. Is water coming out? is it back wash? (D.E. Colored). If no water is coming out with pool back washing, put your ear to the pipe and see if you can hear pressurized water running. Yes? Then it’s likely a clean out on the back wash line to avoid D.E. Blockages. If not then of course you’re left puzzling with the who, what, when, where, why of that pipe in that plumbing run. Be adventuresome bud, you’re not going to figure it out by simply looking at it and you’re not going to break your pool.