It is very, very unlikely that debris like I see in post #188 can get through a working filter....virtually impossible.
I am late to this dance but a filter allowing debris that size to pass through is a broken filter. Whether it is torn laterals, improper assembly or something else, debris that size is just not really possible
I would disregard EVERY other aspect of your repair until I took that filter apart, removed the sand, and discovered how that debris was making it's way through the filter.
If I am overlooking something in this lengthy thread, then I apologize but debris that size cannot get through a properly working filter.