Unless it is broken, the center pipe (standpipe) usually is glued into the manifold. I have never seen an instance where the pipe and manifold are separate. If that is not sealed, then yes, sand can enter the pool, but the fit should be tight enough to prevent that if it was designed that way. I've installed at least 100 S-244T filters. I examine every lateral assembly, as I do with all brands that have this type of internal plumbing, before filling to be sure there are no problems and the standpipe and manifold have always been, essentially, one piece