Given the innovativeness of some of the people on this forum, I'm surprised that I've not seen the subject of a DIY sand pool filter suggested.

If the following are true:
A. Sand filters are not very complex objects
B. Working pressures are not terribly high
C. With sand filters bigger IS better
D. Large capacity name brand filters are ridiculously expensive considering
they are largely just ABS thermoplastic or fiberglass containers
E. Various parts such as multi-valves and diffusers are readily available off
the shelf if needed
F. You're the type of person who likes to accomplish a task for maybe half or
less of the cost of buying retail
G. You used to read or have ever even heard of Mother Earth News

How about coming up with a plan for a large capacity, inexpensive DIY sand filter?