Is this a winterized main drain plug?

[kostia]

in the post http://www.troublefreepool.com/caretaker99-is-this-the-best-it-can-do-t25572.html close to the bottom there are pictures of opened skimmer. I am guessing that the plug is for the main drain? It has a stem pressing on which releases air. Can someone please confirm that this is in fact to the best of their knowledge a main drain plug? Second skimmer has a different plug which I assume is a permanent plug?
Thanks for looking and your help.

 

[Heckpools]

They are actually the same type of plug. In the first pic the plug was installed from inside the skimmer. In the 2nd pic, the builder theaded in the plug from outside the skimmer on the bottom.

Not all builders tie the bottom drain into the skimmer. Usually if the builder runs the bottomdrain line all the way to the filter and not to the skimmer he will install the plug like shown in the last pic.

cant really say for sure if the first plug is for the bottom drain. If its your pool you can remove the plug, and blow air down the line with a good quality shop vac. If you see any air bubbles or water moving near the bottom drains then you know its tied in.

 

[Heckpools]

just noticed the air stem. thats strange... maybe it does run to the bottom drain and the previous home owner put that stem there so he could hookup a compresser and blow out the bottom drain for the winter?

 

[kostia]

I am sure it is not the owner, but whoever was winterizing the pool for him...but that is my guess..