intex plunger valve

I have this little valve thing on both of my Plunger Valves for my Intex Pool, one of them is leaking. Anyone have an idea of what it is and how I stop it from doing so?

Hello, I am pleased to say my therapy pool successfully holds water! All specs are in my signature. Next big task is getting plumbing and equipment hooked up correctly before we end up with a large vat of green goo. I am 99% sure our problem is us; there is that 1% chance we are missing...