I was cleaning the cartridge filter thing for my pool and as I was putting it back in, I saw a black plug thing on the ground. I tried to screw it back in but there weren't that many threads and it didn't really screw in. There is also a rubbery greased ball thing that goes in the hole. I put it back on as best as I could, but when I turned the pump back on it started leaking A LOT! so now the pump is off and I have "placed" the plug in so that air and water don't leak out but it is not secure at all. Plus I can't turn the pump on now. Does anyone know what this part is and what I should do? I am freaking out! My pool is an in-ground saltwater pool, if that is necessary info, I don't know. I'm new to the pool care thing so any help is greatly appreciated!