Reactivating a pool which has laid dormant for 5-6 years. It's an in-ground pool with a vinyl liner, 14 X 28 feet, about 12,000 gallons. It has what I believe is a sand filter, it's a fiberglass vessel 24" in diameter, about 26" tall. Volume comes out at about 5 cubic feet / 36 gallons. I was planning on using my shopvac to remove the old sand (unless there is a preferred method), how much and what kind of sand do I put in this thing? I presume that the piping is full of the same nasty water and black muck that's in the pool, any suggestions on cleaning it?