Re: HELP
If sand only went into the pool just once that is alright. But if it does that again, something is wrong. Really, sand shouldn't ever get into the pool, but now and then when you are first setting things up some sand gets into the wrong place and ends up in the pool.
The black gasket should seal tightly to the pool. The key thing is the gasket on the water side of the wall and how well it seals to the liner. The black gasket on the outside is much less important. The gasket should be free of any nicks or cuts and clean. Any dirt or debris can prevent it from sealing properly. You can also have problems if any of the plastic parts crack, which can happen if you tighten it down too much.