Yesterday I was looking through the paperwork that was left with my pool for the 100th time. And the diagram for the filter showed the attached picture going in the filter. So I went and bought three bags of sand and took my filter apart. The sand came out in clumps and was filled with debris. I rinsed the filter and cleaned the laterals and stand pipe. All internal components were covered with a green slime, so I am glad i did this most likely needed to be done anyway. When I was going to put sand back in the filter I found out wat that piece was for. It is used when replacing sand in your filter, it holds the stand pipe centered and covers the hole so you don't get sand down the stand pipe. On another note, when I moved into this house about a month ago there was a box with all kinds of pool parts in the shed so I assumed that this piece was not installed. Changing the sand was not a hard task, the most complicated part was getting the sand out of the tank because I could not fit anything in the top opening because it is such a small hole. I just tipped the tank on it's side and used my hand to scoop the sand out until I could turn it upside down to pour the remaining sand out, after I removed the lateralis of course.